Mr. Obama first broached the idea with Mr. Emanuel weeks ago, say people familiar with their exchanges. "You’d have my back," he is said to have told Mr. Emanuel. Mr. Obama believes, and the skeptics acknowledge, that few people are better suited for the job on paper.

Mr. Emanuel, who turns 49 this month, knows the White House, having been a senior adviser to President Bill Clinton. In a brief career as an investment banker after that, he made millions and became familiar with Wall Street; in the House, he helped negotiate the government bailout of the financial system that the next president inherits.

And by all accounts, Mr. Emanuel knows Congress like few others; in his second term, in 2006, he engineered House Democrats’ victories to regain the majority. The Democrats in turn elected him as their caucus chairman; he was immediately viewed — not least by himself — as a prospective speaker. A centrist Democrat, Mr. Emanuel knows policies as well as politics, easily distills complex issues into a simple message and is renowned for always seeing several steps ahead in the legislative process.

But there’s the matter of his temperament — or, as Mr. Emanuel says, “I swear a lot.” He also yells a lot, and in his sentences his favorite expletive can serve as subject, verb or adjective when he is facing down either recalcitrant Democrats or Republican opponents. As the House Democrats’ campaign chairman for 2006, he swore at Hispanic and African-American House members, nearly all of whom had safe seats, to contribute more of their personal campaign finances to the party effort. Speaker Nancy Pelosi intervened to smooth things over.

To many Democrats, including some who are close to both men, Mr. Obama’s choice of Mr. Emanuel to run the White House seems at odds with the atmosphere Mr. Obama enforced at his Chicago campaign headquarters. The motto there was “No drama with Obama,” in contrast with the backbiting and shakeups in rivals’ campaigns.