Mr. Bloomberg was described as conflicted about a national run, intrigued by the possibility of winning the presidency but telling friends that he would not run unless he was certain that he could win. And he did not want to go down in history as a spoiler who contributed to the defeat of a Democrat like Senator Hillary Rodham Clinton of New York, he has told friends.

Image Ester Fuchs, a former Bloomberg adviser who remains close. Credit... Ruth Fremson/The New York Times

“He will not run to be a spoiler,” said Ester Fuchs, a special adviser to Mr. Bloomberg in his first term who remains close to the administration.

Even if Mr. Bloomberg in the end does not run, he is now assured of a platform to speak out on national issues and the country’s political climate, a stage that would fortify him as he enters what is normally the lame-duck portion of his term.

That national platform, coupled with Mr. Bloomberg’s vast wealth, means that he does not have to rush to make a decision. The first deadline for filing petitions to qualify for a state ballot is next May in Texas.

Aides involved with other campaigns said they could see a long-shot situation in which Mr. Bloomberg might enter the fray, particularly if the Democratic and Republican presidential candidates emerge as nominees after long and bloody primaries.

“Is it possible?” asked Joe Trippi, who managed Howard Dean’s campaign in 2004 and is now a senior adviser to John Edwards’s campaign. “Yes, I think it is. The hardest thing is making sure you are on the ballot, and he has the resources to do it. The threat of him being in and being a real actor is real, and you have to take that seriously.”