But party rules don't bind delegates to the candidate they've committed to, and Clinton has been dropping the idea that she could poach some Obama delegates as the hard-fought nomination battle goes to the convention in Denver.
"Remember that pledged delegates in most states are not pledged," Clinton told the Daily News editorial board last week. "You know, there is no requirement that anybody vote for anybody. They're just like superdelegates."
While analysts think most pledged delegates are hard-core partisans who won't stray, City Controller Alan Butkovitz, who's running in the primary as a Clinton delegate, said this is a year in which anything could happen.
"What do [Obama] delegates do if Bill Clinton shows up at their house?" Butkovitz asked. "He's the best salesman there is. He's a very potent weapon who brings tremendous emotional power."
"I think that's why the Clintons haven't given up. They know they have lightning in a bottle," Butkovitz said. "You've got two and a half months after the primaries before the convention. If they're 80, 100 votes short, do they think they can pick up a delegate a day?"
Both campaigns will continue to try to woo superdelegates in cases where they see hope for movement.
With U.S. Sen. Bob Casey's endorsement of Obama last week, only seven of the 26 Pennsylvania superdelegates chosen so far - three more won't be named until a party confab in June - haven't publicly committed to a candidate.
But the 14 Clinton supporters and five Obama superdelegates are free to change their minds up until the moment they vote at the convention.
Are pledged delegates just as free?
A national party rule established in 1982 requires pledged delegates to "in all good conscience reflect the sentiments of those who elected them."
