"Hold on a second guys, I was getting all carried away!" Obama said, rushing back to the stage to address New York donors in July. "Sen. Clinton still has some debt. And I could have had some debt if I hadn't won, so I know the drill. There are many supporters of mine here who have not yet given something to help her retire that debt."
Many Obama supporters are loath to help pay off Clinton's reported $10-million debt to Penn, who has been blamed for Clinton's failed "inevitability" campaign strategy in a year when Democratic voters wanted "change."
"I believe she's going to be the nominee," Penn confidently predicted in an interview with ABC News' "Nightline" in September 2007. "I think every day is a good one, and I think that as every day goes on people see that she has the strength and experience to become president."
Clinton's hard-fought battle to become the first woman Democratic nominee fell short and many Obama supporters were insulted by the Clinton campaign's tactics.
Democrats point to former President Bill Clinton's comments early on in the primary characterizing Obama's early Iraq opposition to Iraq as "a big fairy tale."
Things became even more heated when the former president dismissed Obama's South Carolina primary, likening it to Rev. Jesse Jackson's S.C. primary wins in 1984 and 1988.
Their rivalry became so bitter that when Obama finally won enough delegates to clinch the party's nomination, Clinton initially refused to concede the race.
"This has been a long campaign, and I will be making no decisions tonight," she told supporters in New York City on June 3, the night Obama effectively won the nomination.
Her supporters chanted "Denver, Denver, Denver," urging her to fight to the party's convention in August.
But even without Clinton on the ticket, Lehane argues most Clinton supporters will line up behind Obama.
"At the end of the day," Lehane said, "loyal Clinton supporters support her because of the values, ideals and issues she fights for and appreciate that if we want to change the direction of the country that it is a no brainer to get behind Obama and do everything possible to help him win -- regardless of the fact that Hillary is not on the ticket."
ABC News' Jake Tapper contributed to this report.