Aides said time was actually in Mr. Obama’s favor. The longer he demonstrates he can withstand the heat of a national campaign, they say, the more willing party leaders seem to be to embrace him. “What we’re seeing now is a trickle of people making that final decision to publicly commit,” says Jeffrey Berman, Mr. Obama’s chief delegate tracker.

His counterpart for Mrs. Clinton, Harold Ickes, directs 10 staffers working full time to forestall further defections. Mr. Ickes says the campaign can preserve a large enough pool of holdouts for her to rally before the Denver convention.

“Based on what we’re seeing,” Mr. Ickes said, “most of them are waiting and watching and holding their powder.”

Harold M. Ickes was midway through a typical profanity-laced cell-phone call on the inch-by-inch battle for the Democratic presidential nomination recently, when he peered over his glasses and demanded, "This call is off the record, O.K.?"

Would anyone want to pick a fight with Ickes, the famously ill-tempered bad boy of the Democratic Party who once bit a rival political operative on the leg?

Who once got so mad at having to remove his shoes at an airport security line that he marched off to his plane, yelling "Keep them!" over his shoulder, and flew home in his socks? Who sometimes answers reporters' phone calls with a curt "I'm sorry, Mr. Ickes isn't here now," and then simply hangs up?

Ickes isn't fazed by those who accuse him of damaging the party by trying to wrest the nomination away from the first viable African-American contender. "Everyone says, 'You can't take this away from a strong black candidate,'" Ickes says. "Well, how about the first woman candidate of consequence? That's been almost swept under the rug while people have been mesmerized by Obama. Yes, he's a very strong candidate. But so is Hillary. She's a pretty big deal too."

In 1988 Ickes was at it again, negotiating a change in party rules that would not be tested until 2008. In return for Jackson's support at the convention that summer, Michael Dukakis endorsed a complex plan that awarded delegates based on a candidate's proportion of the vote in every state. By doing away with winner-take-all primaries, the new rules prevented a front runner from wrapping up the nomination with a handful of wins in big, delegate-rich states. Underdog candidates could stay alive through the primaries, and perhaps even win the nomination, by collecting delegates in every contest, whether they won it or not. It would be two decades before an underdog turned front runner named Barack Obama would take full advantage of those rules. If Clinton's victories in big states like New York, California, Pennsylvania and Ohio had been winner-take-all, she would be the nominee today. Of course, if superdelegates didn't exist, Obama's delegate lead would be foolproof. Such are the ironic consequences of the rules Ickes helped write.