Not that he has much choice. Mr. Menendez, New Jersey's junior senator, chairs the Democratic Senatorial Campaign Committee, which recruits and provides financial and political support for the party's U.S. Senate candidates. Optimism is part of the job.

But in 2010, Mr. Menendez will have to deal with some unpleasant realities that his predecessor, the irrepressible Chuck Schumer—who chaired the D.S.C.C. in the elections of 2006 and 2008, when Democrats picked up a combined 14 Senate seats and lost no incumbents—never faced.

For one thing, Democrats, with control of the White House and both chambers of Congress for the first time since 1994, are now in something of a defensive crouch. In '06 and '08 they were able to get by just pointing out the (many) shortcomings of George W. Bush. In '10, they'll have to show results.

And then there's history: Losses in a midterm election are almost automatic for the White House's party, which has avoided them only three times since the Civil War. Slippage is even more likely when you consider that the Democrats now (in theory) have 60 seats—the most for either party in 30 years.

The chairman's spin?

"We obviously have the wind not blowing at our back, but blowing a bit in our face," Mr. Menendez told the Observer this week. "But in the face of that, I'm encouraged by a couple of factors."

One of those factors is the high number of seats being vacated by Republican senators--six, three of them in states that Barack Obama won last year (New Hampshire, Florida and Ohio) and one in a state he nearly won (Missouri). The other two Republican vacancies are in Kentucky—a red state, but one where Tea Party fervor could propel Rand Paul, the fringe-y son of Ron, to the G.O.P. Senate nomination, thus creating an unexpected opportunity for Democrats--and Kansas, where Democrats really won't have a chance.

"The Republican retirements have created open seats and pick-up opportunities in five key states," Mr. Menendez said.

Obviously, if the Democrats can win two or three of these races, they'll stand an excellent chance of bucking history. But that's easier said than done. "I don't think the open seats are a given for them," Jennifer Duffy, who analyzes Senate races for the nonpartisan Cook Political Report, said.

The main problem is that while Democrats fared well in states like Ohio and Florida in 2008, they did so under near-ideal conditions. The same formula that worked like a charm last year—pointing fingers and that old stand-by, blaming Mr. Bush—won't get them very far this time around. "When the climate is good for them, (Democrats) can win those states, but it's close," Ms. Duffy said. "In a bad climate, they're going to struggle--and things are not looking that good right now."

This leads into the second factor that Mr. Menendez stresses: Republican infighting. In numerous states, the favored candidates of the G.O.P. establishment are facing serious primary challenges, many of them fueled by the "back-to-basics" conservative revolution being pushed by South Carolina Senator Jim DeMint.

In the post-Bush G.O.P., where mass defections have vested the ideologically extreme base with outsize influence, some of these insurgents could actually win. And even if the insurgents don't win, they could still cause severe damage to the long-term viability of the establishment's preferred candidate.

"Their mainstream candidates--the candidates they'd like to see win--[are] moving more and more to the right, outside the scope of where you want to be in the general election, which is the center," Mr. Menendez said.

Ground zero for this phenomenon is Florida, where national Republican leaders were quick to line up behind Governor Charlie Crist, who had crafted a popular, moderate image, for the seat that Republican Mel Martinez vacated. But conservative activists have mobilized behind Marco Rubio, a charismatic former state House speaker who, according to the most recent Rasmussen poll, is now tied with the governor. Crist has responded by veering sharply to the right-creating hope among Democrats that Rep. Kendrick Meek, their likely candidate, can claim the middle no matter who the G.O.P. nominates.

Something similar may be brewing in New Hampshire, where the state's former attorney general, Kelly Ayotte, is the G.O.P. establishment's choice to run for Judd Gregg's seat. Ms. Ayotte leads Democratic Rep. Paul Hodes in polls—but she's also facing a potentially serious primary challenge from Ovide Lamontagne, a conservative who previously upset the establishment's candidate in the 1996 gubernatorial primary (and then went on to lose the general election in a rout).

G.O.P. primaries also loom in Ohio, Colorado, and Illinois, to name just a few. "These primaries complicate Republican plans because they soak up resources—a lot of money is being spent, [and] many of these candidates will have to spend millions in their primary," Mr. Menendez said.

Of course, while Mr. Menendez generally receives high marks for recruiting strong candidates, there are some potentially problematic primaries on the Democratic side.

The highest-profile of these is in Pennsylvania, where Arlen Specter, whose party switch gave Democrats their 60th Senate seat earlier this year, is being backed to the hilt by the White House and Mr. Menendez's D.S.C.C. But his lead over his primary challenger, Rep. Joe Sestak, keeps narrowing—and in general election match-ups with Republican Pat Toomey, it's a dead heat. Some wonder if national Democrats are propping up a dead horse.

"It's clearly a competitive primary," Mr. Menendez said. "But Arlen Specter is working incredibly hard. He has visited every county in the state, met with every Democratic Party from each and every one of those counties, has been a great addition to our caucus since he arrived...and I think he's going to do very well."

There's also potential primary trouble for Democrats in Ohio, where the D.S.C.C.'s preferred candidate—Lieutenant Governor Lee Fisher—has failed to pull away from his intra-party foe; in Colorado, where appointed incumbent Michael Bennet is being challenged by a former state House Speaker; and in North Carolina, where the D.S.C.C.'s candidate has waffled on whether to run (he finally decided to do it) and now faces a primary against the better-known secretary of state.

And that's not even mentioning New York, where Kirsten Gillibrand has benefited from a concerted effort by the White House, the D.S.C.C. and Mr. Schumer to clear the primary field. And yet, she is still struggling in polls—even trailing. According to a new Quinnipiac poll, New York City Comptroller Bill Thompson bests Ms. Gillibrand by a surprising 13 points. To put that in perspective, Mr. Thompson, who has not announced his plans for 2010, only ran even in an earlier poll against Tom DiNapoli, the unelected and largely unknown state comptroller.

"I'm not fazed by Kirsten's situation," Mr. Menendez said. "She's never run a statewide race. She was from upstate New York, ran in a congressional district, had no exposure statewide, and had no paid media statewide—or even in the heart of the most populous part of the state, New York City, like Thompson has. So I just view it quite differently."

There's also the matter of Connecticut, where nearly everyone agrees that five-term incumbent Chris Dodd can secure the Democratic nomination if he wants it-and that he'll lose in the fall if he does.

"This is an incumbent where, if you're giving (national Democrats) a little sodium pentothal, they would like him to get out of the race," Ms. Duffy observed.

Mr. Dodd has been beaten relentlessly for his closeness to the financial services industry and has emerged as a popular scapegoat-in Connecticut and nationally-for the sub-prime mortgage catastrophe and subsequent Wall Street meltdown. He's already spent heavily on ads and has been campaigning hard, but polls show him floundering, losing by double-digits to his most likely G.O.P. foe.

The obvious parallel is to Robert Torricelli, the former New Jersey senator who waged a re-election campaign against similarly dire poll numbers (and in a similarly blue state) in 2002—until party leaders, fearful of losing a seat they never should lose, convinced him to drop out five weeks before the election. In Mr. Dodd's case, Democrats would have an obvious replacement candidate—Connecticut's mega-popular attorney general, Richard Blumenthal—who would likely crush any Republican candidate.

Mr. Menendez, who was actually offered the chance to replace Mr. Torricelli on the ballot that year (and declined), said that "as far as I know, (Dodd) is absolutely intending to go all the way."

Still, he didn't speak of Mr. Dodd's continued candidacy as a foregone conclusion, saying, "I believe that at the end of the day, we will find that as Chris continues to work it, if he chooses to run, he'll be in position to stir a strong reservoir of support that has been developed over years...and can succeed if he chooses to do so."

All told, Democrats and Republicans will be defending 18 seats next November. Earlier this year, at the height of Mr. Obama's honeymoon (and with the G.O.P. brand in utter disrepair), Democrats giddily talked of adding to their Senate majority. Now, with unemployment stuck in double-digits and voters showing impatience with Mr. Obama and his party, Ms. Duffy said they'll do well to break even next fall—"and with every day that the environment does not improve for them, their chances of keeping 60 get worse."

Mr. Menendez, ever the optimist, said that Democrats will show results on health care and jobs over the next year—with no help from the Republicans. "And if we make the progress that we've already begun to see and that I believe we will make on health care reform, they're going to have been the party of opposition, not the party of any constructive ideas," he said. "And they will have ceded the most important issues to us."

Obama acknowledged the validity of this concern and then explained why he doesn’t share it. His main point: that a public plan that has to play by the same rules as private insurance companies will have no unfair advantages, which should allow for healthy competition.

Whatever you think of each man’s position, the exchange was respectful, substantive, and rational—a reasonable concern answered with a reasonable argument; two intelligent people with a reasonable disagreement.

Now, contrast that scene to what played out just hours earlier in Pennsylvania, where Senator Arlen Specter held a town hall meeting of his own. The crowd, much smaller (not surprisingly) than at the Obama event, was filled with furious reform opponents united mainly in their hysterical irrationality. Their arguments, even when expressed with relative calm, were laced with misinformation, faulty assumptions, and baffling leaps of logic.

There was, for instance, the woman who, her voice quivering with rage, told Specter that she’d been apolitical until recently but that the health care reform effort was part of “a systematic dismantling of this country…I don't want this country turning into Russia, turning into a socialized country. What are you going to do to restore this country back to what our founders created, according to the Constitution?”

“You ask me to defend the Constitution—that’s what I’ve been doing,” Specter replied, a comment that provoked a torrent of screams from the crowd. Seated a few feet away, the woman’s eyes widened as she shouted, “WHAT?” (Maybe Specter was referring, in part, to his courageous vote against Robert Bork’s Supreme Court nomination in 1987. Not that this outraged citizen would know or care about this—by her own admission, she only just started paying attention.)

Shortly thereafter, an angry man grabbed a microphone and unleashed a whale of a tirade, closing with an ominous warning: “One day, God is going to stand before you, and he’s going to judge you and the rest of your damn cronies up on the Hill, and then you’ll get your just desserts. I’m leaving.” The crowd roared its support.

But the irrationality of the Pennsylvania crowd was best articulated by a man who, in an apparent effort to sound reasonable, assured Specter that he did want to see health care reform—“but not this.” Then, before he dove further into his rant, Specter called his bluff: If not this, he asked, what kind of reform would you support?

The man hesitated, then finally recommended the following steps: enact tort reform, round up all of the illegal immigrants and send them home, and impose term limits on Congress.

This was very telling. Tort reform, long a favorite of the right, has been pushed relentlessly by the usual right-wing suspects (like these two fellows) as a key aspect of any reform. Never mind that malpractice costs—both in payouts and premiums—account for a tiny (less than one-percent share) of overall health care costs and that the states that have adopted tort reform have enjoyed no reduction in health care costs.

But at least tort reform is somewhat related to health care, in that it involves doctors. The man’s other suggestions—round up the illegals and give us term limits!—are totally unrelated. His exchange with Specter was the exact opposite of Obama’s with the Republican in New Hampshire: substance-free and rooted in paranoia that has noting to with health care.

Specter’s experience, of course, is consistent with the experiences his fellow Democratic senators and House members have had holding town halls—something that has been well documented by the media.

It would be easy to say that the tone of the Obama event was different simply because he’s the president, and as such automatically commands more respect from an audience than a mere member of Congress. No doubt, this was part of it.

And it would be fair to note that the White House, unlike the office of a random senator or House member, was able to choreograph the event in a way the ensured a more friendly crowd.

It was no accident, for instance, that when Obama finished his opening remarks, he was greeted by a standing ovation from what (on television, at least) appeared to be 75 percent of the audience. And a question from a random young girl—who asked Obama to dispel all of the bad things that protesters outside were saying about him—was rather suspicious.

Still, he did receive several questions from citizens who expressed rational, substance-based concerns about health care reform. This kind of skeptical-but-intelligent dialogue was all but absent from the Specter event, just as it’s been absent from most other recent town halls.

This is further evidence that the non-presidential town halls have functioned largely as an echo chamber for the most passionate and motivated segment of the electorate: angry rejectionists who feel instinctively threatened by Obama and who have been resisting his legitimacy since the moment he was elected. Really, it’s not hard to imagine the man who lectured Specter about God’s wrath cheering at a McCain-Palin rally last fall, screaming about Obama’s “socialist” agenda. 

The mistake that’s been made by the media has been to lump the irrational rejectionists in with the much broader chunk of the electorate that supports the concept of health care reform but is uneasy with what they’re now hearing out of Washington. The first group will never—ever—support an Obama-led reform effort; the second group is largely open to doing so, but wants some questions answered first.

What’s frustrating, of course, is the enthusiasm gap between these two groups. The rejectionists are fundamentally committed to stopping Obama; hence, their mobilization for even the most obscure House Democrat’s town hall meeting. They’re smaller but louder.

The other group is less committed and more muddled in its views; it takes a presidential visit to bring them out. But Obama came face-to-face with a few of them today, and the difference was refreshing.

The letter writers are  Senators Sherrod Brown (D-Ohio), Debbie Stabenow (D-Mich), Russell D. Feingold (D-Wisc.), Carl Levin (D-Mich.), Evan Bayh (D-Ind.), Robert P. Casey (D-Pa.), Robert C. Byrd (D-W.V.), Arlen Specter (D-Pa.), John D. Rockefeller IV (D-W.V), and Al Franken (D-Minn). In the letter, these Senators express:
“… strong support for the inclusion of a package of initiatives, including a border adjustment mechanism, to ensure the viability and effectiveness of any climate change policy crafted by Congress… As Congress considers energy and climate legislation, it is important that such a bill include provisions to maintain a level playing field for American manufacturing…
Measures to ensure that U.S. manufacturers do not bear the brunt of our climate change policy could include: short-term transition assistance in the form of rebates provided to energy-intensive and trade-exposed industries; negotiating objectives requiring any international agreement to address manufacturing competiveness; effective means to measure, monitor, verify, and hold countries accountable for emissions reductions; and policies that promote investments in energy efficient and clean technology manufacturing and help the sector retool for the clean energy economy.”

This is a key issue, and if not addressed it has the potential to split the Democratic Party in two and to eliminate the possibility of climate regulation both here and throughout the world. The underlying cause of this issue is the uneven pattern of economic development worldwide. The developed nations built their economies on fossil fuels and never had to worry about greenhouse gases. Nations just now building their economies, such as India and China, want the same “right to develop” that the world’s wealthy nations had back in the 20th century. The perspective of American manufacturers is that if they have to comply with these new regulations, then everyone else should as well. They assume that compliance with greenhouse gas regulations will raise the price of their goods and services.  They propose tariffs as a method of equalizing prices and “leveling the playing field.” Tariffs, of course, interrupt the free trade of goods, restrain competition and ultimately reduce wealth. 

It seems to me that the solution is not to raise the cost of imported goods, but rather to use the tax code and innovative federally funded research to lower the cost of compliance with new global warming rules. We should not automatically assume that cleaner manufacturing is inherently more expensive. While this tends to be true when we retrofit old factories with pollution control equipment, we can encourage the construction of new facilities that have a smaller carbon footprint from the start. But where will the money come from for this?

One source might be the funds raised by the auction of emission allowances under Waxman-Markey.  A second source requires that we break the taboo on new taxes and levy a new tax on fossil fuels. This money could then fund a tax deduction or credit for investments in technology that reduce greenhouse gas emissions. In addition, we can reduce emissions from Midwestern manufacturers by targeting new renewable energy sources for manufacturing. We can also fund research on carbon capture and storage that will enable us to burn fossil fuels without impacting climate systems.

Rather than wasting time protecting old and dirty factories, we should fund the research needed to revitalize American manufacturing. We should use the tax code to encourage investment in manufacturing facilities that can compete with the foreign factories that rely on cheaper labor and less stringent environmental laws. We should work to build lower-cost, non-fossil fuel energy sources and more automated factories engineered to reduce waste and emissions.

It is disappointing, but not surprising, to see these Senators “rounding up the usual suspects.” It is really time to break this depressing cycle of rust belt protectionism and anti-environmentalism. One look at Detroit tells you how successful this strategy has been. If we are going to get the developing world to build their industries according to green principles, the United States must lead by example. We need to develop green technology, implement it at home and provide incentives for adopting it in the developing world.

This is not an argument for allowing our industrial base to disintegrate. We need to stimulate private investment in that base and directly fund the research and development required to build a competitive but sustainable economy. While this letter to the President is simply an opening gambit in the intense bargaining process that awaits us this fall, it is both pathetic and short-sighted. These folks know better, and rather than providing vision and forward-looking leadership, they have decided to protect their flanks. It is high time that we focus on the fundamentals--which even these senators acknowledged when they wrote: “Climate change is a reality and the world cannot afford inaction.”  At least they got that part right.

It’s an absurd dance. Voters like hearing about “independence” and “bipartisanship,” so candidates indulge them, only to take office and immediately morph into the party-line loyalists they just spent a year swearing that they weren’t. There are some exceptions to this rule (Arlen Specter comes to mind), but by and large, you can predict how more than 90 percent of senators and House members will vote on anything just by their party label.

Why, then, do we pretend the same phenomenon doesn’t apply to Supreme Court justices?

For the last few days, Jeff Sessions, the ranking Republican on the Senate Judiciary Committee, has led his party’s attack on Sonia Sotomayor. In part by repeating her “wise Latina woman” remark from 2001 over and over, Sessions (with help from his fellow Republicans) has sought to disqualify Sotomayor on the grounds that she holds personal biases that will make it impossible for her to interpret the law impartially. As Sessions put it on Wednesday, his concern is “whether agendas are being promoted through the law rather than just strictly following what the law says.”

Therein lies the absurdity of this and every Supreme Court confirmation hearing—but this one in particular. Sessions assumes that there’s only one correct way to decide every Supreme Court case and that “the law” makes it absolutely clear what that way is—which is like saying there’s only correct way to vote on any piece of legislation in Congress and that there exists a clear, exact, and unimpeachable source for divining what that way is.

But that’s ridiculous. On any given issue, Democrats in Congress will see the right decision one way, and conservatives the other. Both will insist that the facts are on their side, both will swear they are motivated by the best interests of the people, and both will claim they are simply adhering to the oath they took upon assuming office.

This is to be expected. No matter what they said about independence in their campaigns, most members of Congress are either generally liberal or generally conservative and most important votes in Congress can be reduced to a liberal and conservative position. So the same people who as candidates insisted they’d put the people over their party wind up voting with their party 99 percent of the time once in office.

Now, consider the Supreme Court. Just like the voters who want to hear all about bipartisanship from Congressional candidates, senators love hearing all about “fidelity to the law” (which Sotomayor has repeatedly pledged this week) from Supreme Court nominees. And yet, just like with members of Congress, we can tell on pretty much every contentious case before the Supreme Court how every justice will vote—and it’s almost always in accordance with the ideology associated with the party of the president who nominated him or her.

The most famous example of this is the Bush v. Gore case that settled the 2000 election. Before then, there had never been any partisan or ideological divide on the issues at the heart of the Florida recount. But the fault-line quickly emerged, with conservatives shouting for legal interpretations that favored George W. Bush and liberals pushing for those that would benefit Al Gore. Rest assured, had it been Gore who led the initial Florida count and Bush who had been victimized by hanging chads, each side would have passionately embraced the opposite view.

When the matter finally reached the Supreme Court, the most reliably conservative justices (William Rehnquist, Antonin Scalia, Clarence Thomas, Anthony Kennedy, and Sandra Day O’Connor) all sided with the conservative/Republican argument, while its four liberal members (John Paul Stevens, Ruth Bader Ginsburg, Stephen Breyer and David Souter) all voted for the liberal/Democratic case. (Yes, Stevens and Souter were Republican appointees, but just like Congress has the occasional liberal Republican or conservative Democrat, so does the court.)

And this is the norm for the Supreme Court. Sure, there are plenty of 7-2 and even 9-0 rulings, just like the House has its share of 431-4 votes. But by and large, especially with momentous cases, you can accurately predict well ahead of time how virtually every justice will vote. Mind you, those justices would all surely insist that they are simply adhering to the law, to the Constitution, and to the oaths that they took. But just like members of Congress, what they are really doing is making ideology-influenced interpretations.

There’s every reason to believe that Sotomayor will interpret the law from a generally liberal perspective. That’s why Barack Obama picked her. Just like there was every reason to believe that John Roberts and Samuel Alito, Bush’s two Supreme Court picks, would interpret the law from a conservative perspective—which they have. An ideology is nothing more than the accumulation of a lifetime’s worth of “biases.” Every justice brings one to the court, just like every congressman brings one to the House and every senator brings one to the Senate.

Sessions’ argument is disingenuous. His concept of “following what the law says” is as subjective as Sotomayor’s, or anyone else’s. It’s also as predictable. Were Sessions on the court, we’d have little trouble guessing how he’d vote in most cases—just as we have little trouble guessing how he’ll vote on anything in the Senate now. 

Sessions is really bothered by Sotomayor because she’s probably a liberal. He also may be bothered by her ethnicity. Wouldn’t it be nice if he could drop the ridiculous language about “agendas” and just say so?

In the fall of 1991, the political right was gunning for Arlen Specter. Four years earlier, he’d infuriated them by lending a critical assist to the successful campaign to kill Robert Bork’s Supreme Court nomination and he’d done little in the intervening time to make peace with them. Now, with Specter facing reelection in 1992, they were threatening him with a primary challenge.

Specter seemed likely to withstand the challenge from Stephen Friend, a staunchly conservative state legislator, but he wasn’t in the mood to take chances. So when Clarence Thomas, George H. W. Bush’s choice to replace Thurgood Marshall on the Supreme Court, was threatened by sexual harassment charges from Anita Hill, Specter took it upon himself to act as Thomas’ de facto defense attorney.

With the cameras rolling and the nation transfixed, he subjected Hill to a withering cross-examination, repeatedly challenging her account and accusing her of perjury. The gambit worked—sort of. It bought Specter the intraparty reprieve he’d wanted (in the April ’92 primary, he crushed Friend by a two-to-one margin), but his boorish treatment of Hill turned female voters against him and brought Lynn Yeakel, a previously unknown fund-raiser for women’s causes, to the brink of victory in the general election. As always, though, Specter survived in the end.

Now, nearly 18 years later, Specter again sees a high-profile Supreme Court nomination as the perfect means to make amends with his party’s restive base. Except this time, thanks to his switch to the Democratic Party, the base is on the left, and not the right.

This weekend, he appeared on Fox News Sunday to discuss the nomination of Sonia Sotomayor for the Supreme Court. Had he not switched parties in April, it’s possible, maybe even likely, that he would have used this forum to amplify Republican objections to Sotomayor—namely, that her ruling on an affirmative action case and a 2001 speech show her to be an “activist judge” who is obsessed with race. After all, until his switch, Specter was facing a serious challenge (far more serious than Friend’s in ’92) from former representative Pat Toomey. So Sotomayor’s nomination would have offered him a chance to score some points with a skeptical G.O.P. base.

But now it’s the Democratic primary that Specter must worry about. And despite the best efforts of party leaders in Washington and Pennsylvania, it looks like he’ll face a challenge next spring from Joe Sestak, an ambitious and well-funded congressman from the Philadelphia suburbs. Uh-oh. Better brush up on those pro-Sotomayor talking points!

Actually, Specter recited them quite nicely. After Lindsey Graham utilized a context-free interpretation to Sotomayor’s 2001 speech to claim that Sotomayor had claimed that “somebody with her background would be a better judge than a guy like me, a white guy from South Carolina,” Specter rallied to her defense.

President Obama was looking for diversity, he said, “and I think Judge Sotomayor brings that. But let’s put her comment in context with the whole speech, and it didn’t stand out all that much in context. And further, put it in context with her whole record. She has an extraordinary academic record—Princeton and Yale, a prosecutor, have experience in international trade matters, on the district court, trial court experience, circuit court of appeals.

“So she has an extraordinary record. And I believe that it’s fair to ask her about the question, but she has a long solid record to show that she’s fair and not biased.”

Host Chris Wallace pressed Specter about Sotomayor’s speech, but Specter wouldn’t budge.

“She meant that somebody with her experience has something to add,” he said, pointing out how almost uniformly white and male the Supreme Court has historically been.

“If you go back to the Supreme Court discussion room—very small room, small table, nine people sit around and decide monumental questions. And the diversity and the point of view of Latina woman is significant. It adds to the mix.”

Specter also defended Sotomayor on her ruling as an appeals judge in favor of a New Haven affirmative action program, a decision that the right is using in an effort to paint her as a Lani Guinier-esque “quota queen,” and insisted that she meets the same standards that he applied when he voted to confirm John Roberts in 2005.

Of course, Specter steadfastly denied that his view has anything to do with mollifying his new party’s base. He reminded Wallace that he’d opposed Bork, “one of the most highly touted nominees ever for the Supreme Court by a Republican president,” and maintained that he is “duty-bound under the Constitution to exercise independent judgment under separation of powers.”

The reality is more complicated. That Specter is backing Sotomayor does seem generally consistent with the impulses that hurt him when he was a Republican (for instance, opposing Bork). Free of all political pressures, it would be fair to assume that Specter would support Sotomayor. But it’s also fair to question whether he would have shredded Anita Hill in 1991 had he not been facing a G.O.P. primary threat. And it’s equally fair to note that his partisan conversion hasn’t gone as well as he initially anticipated—making it more urgent that he find a way to make good with the base.

With Barack Obama, Joe Biden and Ed Rendell all enthusiastically on board, Specter seemed to assume that rank-and-file Democratic support would automatically follow and, as a result, spent his first few weeks as a Democrat needlessly antagonizing the party base—seeming to endorse Norm Coleman’s recount efforts in Minnesota, among other slights. He’s since been disabused of that notion, with Democrats in the Senate denying his bid to retain his seniority (at least through 2010) and with Sestak seizing on liberal unrest to justify a primary challenge.

For decades, Specter’s game has been to vote his conscience when he can get away with it and to throw red meat to the base whenever the next primary is approaching—as it now is. So, whether he personally likes and believes in Sotomayor really isn’t the issue right now. He has no choice, and he knows it.    

And that's just what Specter's critics, on the right, on the left, and in the middle, have been doing this week.

"Self-preservation in the first order" and "a cold, crass political calculation" is how G.O.P. chairman Michael Steele described Specter's switch, while Joe Sestak, a Pennsylvania Democrat who is threatening to challenge Specter in next year's primary, pointedly asked, "Is that the type of individual we want?"

On The Daily Show, Jon Stewart rolled tape of Specter's press conference earlier that day, at which the senator bluntly stated: "The prospects for winning the Republican primary are bleak. I am not prepared to have my 29-year record in the United States Senate decided by the Pennsylvania Republican primary electorate."

"How refreshing is that?" Stewart asked sarcastically, before impersonating Specter's voice and saying: "I just want to be clear: Principle played no part in this decision. This was politics. I like my job."

The irony, though, is this: Specter's defection, while immediately necessitated by self-preservation, was a direct result of his willingness to take principled stands.

What Specter's critics, perhaps intentionally in some cases, are failing to take into account is why his political career reached the point it did this week, when jumping to the Democrats emerged as his only realistic means to survive. (A G.O.P. primary poll taken days before Specter made his switch showed Pat Toomey, who came within two points of knocking Specter off in the 2004 Republican primary, ahead by a staggering 21 points—about as bad as it can possibly get for an incumbent senator in a primary.) The reason, of course, is because he's put principle above partisan politics more often—and on more consequential votes—than just about any senator in recent history.

For instance, he played a crucial role 22 years ago in defeating Ronald Reagan's nomination of Robert Bork for the Supreme Court. When Reagan announced his choice of Bork, a circuit court judge who had long been admired by the right (and feared by the left), in July 1987, it marked an effort not just to place an outspoken conservative on the court, but also to reignite the Reagan revolution itself, which had run out of steam in the wake of the Iran-Contra scandal and the Democrats' success in the 1986 midterm elections.

Bork's opponents were in a tough spot, though. His writings had been radical, but his resume and legal credentials—to say nothing of his intellect—were impeccable, and there was no modern precedent for denying confirmation to a Supreme Court nominee on purely ideological grounds. Specter, a former prosecutor, used his perch on the Judiciary Committee to question Bork for hours in hearings that received extensive national coverage.

Viewers may not have understood the nuances of this grilling—Specter quizzed Bork about "original intent," "Madisonian majoritarianism," and Oliver Wendell Holmes' "clear and present danger" free-speech standard—but when Specter concluded by announcing that he couldn't support Bork, it gave considerable cover to other wavering senators to join him, which they did: Bork's nomination was defeated, 58 to 42. And the Reagan revolution never really recovered.

Conservatives, of course, were furious. Robert Walker, a devoutly conservative Pennsylvania congressman, called Specter's Bork vote "a Panama Canal kind of issue," a comparison to the late '70s treaty that cost several Republicans their careers. But Specter survived the Republican primary when he ran again in 1992, defeating a conservative state representative by 30 points.

The Bork battle stands as one of Specter's most visible and consequential breaks from the G.O.P. line, but it was hardly the first or only example. Two years before Bork, he'd announced his opposition to Reagan's MX missile program, once again enraging the hawkish, Reagan-loving right. In response, the White House threatened to cut off all national Republican money from Specter's 1986 reelection campaign.

He's always been pro-choice, even mounting a presidential campaign in 1996 in which he pitched himself as a vehicle for cultural moderates who were fed up with the religious right. He raised no money, received scant media coverage—and was showered with boos by G.O.P. audiences whenever he made his case. It was a futile campaign, but one that was, however disastrously, about principle.

And, of course, there was this year's vote on the stimulus bill. The entire Republican establishment and every conservative activist group turned opposition into an article faith, treating the issue as a debate over the future of capitalism, freedom and democracy. When the bill reached the Senate, Specter knew he could have simply joined that chorus and saved his career. At the time, Toomey was publicly saying that he wouldn't run. Conservatives, it was clear, were likely to give Specter a pass in the 2010 primary—however grudgingly—if he would play ball with them on opposing Barack Obama's agenda.

And yet Specter negotiated some changes and then voted for the bill. Conservatives called him a traitor (and worse) and, within days, Toomey was in the race—and pulling away in the polls. In raw political terms, Specter's decision was an act of career suicide: Isn't that the very definition of principle?

For some odd reason, Chris Matthews (who earlier this year flirted with challenging Specter in Pennsylvania in 2010) went on MSNBC on Tuesday night and did his best to move the Specter-is-unprincipled ball down the field. In an embarrassingly self-flattering rant in which he patted himself on the back for refusing to "eat it" by signing on to one party's complete agenda, Matthews said that Specter is "the opposite of Edmund Burke—he doesn't stand for the people, he goes with the flow."

Pennsylvanians, Matthews predicted, will see in Specter a man "who was loyal to a political party for a half a century that gave him elective office time after time after time ... and then just like that when he sees a better opportunity, he splits to the other side. You've got to wonder about a guy's character who does that!"

Was Matthews not watching these past three decades, when Specter, time and again, was brazenly disloyal to the G.O.P. and voted his conscience instead? Does he not understand that the only reason Specter now sees "a better opportunity" in the Democratic Party is because he has voted with that party—and against the Republicans—on so many critical issues?

Sure, Specter is trying to save his career. But the only reason his career was in such danger is that, apparently, there's no room in his old party anymore for a principled moderate.