Those political juggernauts were limited to the five boroughs. In his potential conquest of all 50 states, Mr. Bloomberg has said privately that he could spend upward of $500 million, and his aides don’t exactly resist suggestions that his expenditures could approach a full billion.

For political professionals, the prospect of a billion-dollar Presidential campaign—made somewhat more real by the Mayor’s recent change of registration from Republican to independent—is the stuff of fantasy.

“You can take the New York City model, and you duplicate that in other cities,” said Mark Benoit, a Democratic operative who ran Representative Anthony Weiner’s 2005 New York City Mayoral campaign.

Mr. Benoit predicted widespread polling that would constantly measure the shifting attitudes of voters on every significant issue—and make some fortunate pollsters very, very rich. “It’s a consultant’s dream,” Mr. Benoit said. “It’s Christmas and Hanukkah and Kwanzaa all at once.”

In 2005, Mr. Bloomberg paid the polling and political consulting firm Penn, Schoen & Berland Associates $17.3 million, or about 20 percent of his total campaign expenditures, to find out exactly what New York City voters wanted in a Mayor. If Mr. Bloomberg spends $1 billion on a Presidential run, and Mr. Bloomberg’s pollsters get a similar chunk of the campaign budget, they stand to make $200 million.

In 2005, the media-advertising gurus at Squier Knapp Dunn earned an undisclosed percentage of Mr. Bloomberg’s $40.5 million media expenditure. In a Presidential race, the cut is usually about 7 percent, which would translate into an enormous payday given Mr. Bloomberg’s practice of bombarding voters with ads. And the direct-mail experts at the Baughhman Company, who made $4.9 million of the Mayor’s money, must surely be salivating at the prospect of licking so many more millions of envelopes.

Mr. Bloomberg’s New York campaign boggled the minds of even the most veteran political observers.

While his Democratic opponents—Mark Green in 2001 and Fernando Ferrer in 2005—scrounged for cash to keep their campaigns afloat, Mr. Bloomberg flooded the entire city with advertising. In 2001, the post–Sept. 11 spot of Rudy Giuliani embracing Mr. Bloomberg played on a seemingly incessant loop. In 2005, his ads appeared in every weekly newspaper in the city (he appeared in not one, but two, Ecuadorian papers) and his campaign literature was translated into more than 100 languages targeting local ethnic communities.

And then, there is TV.

A Democratic media consultant with Presidential campaign experience guessed that Mr. Bloomberg would simultaneously advertise on national network television, an expensive practice candidates have abandoned since 1988, and target individual markets more microscopically than any candidate ever dreamed.

Judging from his 2005 race, the consultant said, Mr. Bloomberg might target ads at the Arab-American community in Michigan, the German-American community in Milwaukee and each of the country’s distinct Spanish-speaking populations, which are usually addressed as one block.

“The ability to slice and dice down to that level is something candidates don’t have,” said the consultant. “The major advantage it gives you is the ability to never have to make the really tough decisions about where to compete.”

In the battleground state of West Virginia alone, the consultant foresees Mr. Bloomberg airing as many as 14 different ads. The Mayor’s money would also force the Republican and Democratic nominees to spend more. For example, advertising for a state campaign in California runs between $40 million and $80 million. Presidential nominees usually don’t spend a cent there, because it is viewed as so solidly Democratic. But Mr. Bloomberg’s aggressive advertising would compel Democrats to defend themselves with a media campaign of their own. Republicans, sensing an opportunity, would advertise there too.

Hank Sheinkopf, who helped run the campaign of Mr. Green in 2001, has seen the crushing power of Mr. Bloomberg’s millions up close.

Based on the premise of a billion-dollar budget, he thinks that Mr. Bloomberg would spend about $650 million on television, radio and Internet ads that would introduce the Mayor to voters around the country and assure them, as only television can do, that his candidacy is for real. He also foresees a $45 million polling operation to improve Mr. Bloomberg’s coveted voter database.

“Underestimating him is a major mistake,” said Mr. Sheinkopf, who argued that Mr. Bloomberg’s money granted him unparalleled freedom. “That’s the difference. And he can make your money more dear to you, because the fact of having it allows him to do certain things that drive up your cost and make you spend more.”

In 2001, Mr. Bloomberg’s enormous television buy essentially drove up the price of air time for his rivals and prevented them from gaining any traction with voters.

“They can do the mail, the call, the knock and TV,” said Mr. Benoit. “In Bloomberg’s case, he can do skywriting.”

For now, the announced candidates are seeking refuge in the notion that none of the independent candidates in recent elections have managed to rise above the spoiler role.

On Thursday, John Edwards was asked about the consequences of the Bloomberg billion at an event at Cooper Union.

“It’s obvious that somebody like Mayor Bloomberg, who has significant wealth, can have a real impact on the process,” said Mr. Edwards, who went on to advocate public financing for Presidential campaigns. With “a billion dollars of his own money, without a doubt he’d get heard. That doesn’t mean—as you know, an independent candidacy has not faired well in recent years.”

Mr. Bloomberg’s potential run is often compared to that of Ross Perot, the similarly diminutive Texas billionaire who ran an independent campaign in 1992.

But besides the fact that Mr. Bloomberg seems somewhat less eccentric than the Texan (“Eagles don’t flock, you have to find them one at a time,” was one typical Perotism) there is another key distinction.

“Michael Bloomberg is really willing to spend the money,” said Rob Ryan, a Republican operative who managed George Pataki’s first campaign for Governor. “He can be on TV all the time, sending direct mail into key areas, wherever his polling shows he has support.”

Mr. Ryan said that one potential stumbling block for the Mayor would be a lack of foot soldiers available to set the campaign in motion. Some states require tens of thousands of petitions to get on the ballot, which in turn require an enthusiastic and organized grassroots operation.

And as one New York Democratic operative put it, “Right now there is a paucity of talent out there. If you were to jump in and build a 50-state strategy, the people you would be talking to would be the outsiders and the wackos.”

And all of that money also poses its own unique problem, said the operative, who pointed out that it is one thing to keep an eye on campaign expenditures in the Bronx, while it’s wholly another to know what’s happening to the fat check you sent to North Dakota.

“You have to have robust controls to make sure people aren’t pissing your money away,” the operative said.

Still, $1 billion is a lot of money to go through. And as Mr. Bloomberg proved when he simply overwhelmed his opponents in 2001 and 2005, there’s a lot to be said for volume.

As Mr. Sheinkopf put it, “It will be the most sustained television campaign probably over the most protracted period of time in the history of American politics.”

Consider yourself warned.