This, at least, is what Robert Shrum, one of the architects of Mr. Kerry’s fruitless White House campaign, claims in his new memoir, No Excuses.

A President Kerry, Mr. Shrum reveals, would have communicated “in confidence” to France, Germany and other allies with an economic stake in Middle East stability an ultimatum: “If they didn’t send enough troops to form a true multinational force, one not dominated by the United States, then we would withdraw our troops in three to six months.”

The candidate dared not speak this during the campaign, Mr. Shrum explains, because those same allies would have felt immediate public pressure to reject the plan, which Mr. Kerry’s Republican foes would have simultaneously demagogued as a “cut-and-run” scheme that would offer the despised French veto power over U.S. foreign policy.

“Kerry’s notion,” Mr. Shrum concludes, “was the kind of policy that can only succeed once you are already president.”

Fair enough, although it strains the imagination to envision the Kerry plan, had it been implemented, altering the fundamental realities that have made the occupation such a bloody misadventure.

But Mr. Shrum’s broader point—that there is a fundamental incompatibility between serious discussions of foreign policy and domestic electoral politics—is well taken. Mr. Kerry would absolutely have been shredded had he advanced his “secret plan” during the campaign, and for all the wrong reasons. Recall that a Harris poll just two weeks before the 2004 election found that 62 percent of Americans believed Saddam Hussein had “strong links” to Al Qaeda. The gap between the public’s perception and foreign-policy realities was staggering.

Mr. Kerry’s calculation feels duplicitous. Every candidate for the Presidency owes it to the public, one would like to think, to level with them over how he or she will handle a matter as consequential as war.

But it’s also worth recognizing that Mr. Kerry’s approach has actually been the norm for America’s wartime Presidents, who have instinctively understood the limits of the foreign-policy rhetoric the public is capable of stomaching—and who often engaged in foreign affairs in a way completely at odds with their campaign themes.

Woodrow Wilson, who stood on the sidelines as Europe went up in flames during his first term, knew there would be no second term if he talked about plunging American troops into the conflict. Instead, he campaigned for re-election in 1916 under the slogan “He kept us out of war,” which was just enough—barely—to fend off Republican Charles Evans Hughes, whom Wilson’s campaign ironically charged with secretly planning to enter the European conflict. Three months into his second term, though, Wilson asked Congress to declare war on Germany, and American forces ended up playing a pivotal role in thwarting a German advance that nearly gobbled up Paris.

The future of Europe was again at stake in 1940, when Franklin Roosevelt sought a third term against a backdrop of Nazi expansion that many Americans were happy to ignore. Facing vicious attacks from isolationists like Charles Lindbergh and popular sentiment that the war was none of America’s business, Roosevelt felt compelled to declare that he would not send American boys into any foreign wars—even as he instituted a military draft. Upon his 1941 inauguration, Roosevelt, of course, only intensified his war preparations—and there are few now who argue the United States picked the wrong President in the election of ’40.

It doesn’t always work out so well, though.

Nixon’s “secret plan” was a bald political ploy to convince Americans that the intractable Vietnam quagmire could be resolved if only they’d invest their blind faith in him. They did, but his plan amounted to little more than “Vietnamization” and an expansion of the war into Laos and Cambodia.

Before Nixon, there was L.B.J., who stole a line from W.H. Auden in a brutal 1964 ad that tagged Barry Goldwater as the warmonger in their campaign: “We must either love each other or we must die.” But it was Johnson who would radically escalate the Vietnam War in the years ahead.

And then there was Mr. Kerry’s ’04 foe, George W. Bush, who actually won the White House over Al Gore in 2000 in part by saying: “I’m worried about an opponent who uses nation-building and the military in the same sentence.”

Now, much attention is correctly being paid to the 2008 candidates’ posturing on the Iraq question. But if the story of John Kerry’s secret Iraq plan teaches us one thing, it is this:

We may not be learning as much as we think.