Hillary Clinton will address the Democratic convention tonight in a speech designed to mend a lingering party rift and persuade her die-hard supporters to get behind Barack Obama's White House bid.
Mr Obama hopes her high-profile appearance can begin to heal the wounds of a bruising nominating battle and win over intransigent Clinton supporters still angry over his triumph and his choice of Joe Biden over her for his running mate.
The drama cast a shadow over yesterday's opening day of the convention to crown Mr Obama (47) a first-term Illinois senator, as the party's leader and presidential candidate in the November 4th election battle with Republican John McCain.
Mr Obama had tried to ease the tension by giving Clinton, a New York senator, and her husband, former President Bill Clinton, major roles at the convention. Bill Clinton will address the Democrats tomorrow.
"There are going to be some of Senator Clinton's supporters who we're going to have to work hard to persuade to come on board. That's not surprising," Mr Obama told reporters yesterday.
"But if you take a look, I think, at this week, I am absolutely convinced that both Hillary Clinton and Bill Clinton understand the stakes."
Ms Clinton will be symbolically nominated for president tomorrow, although she is expected to release her delegates to Mr Obama after a roll call vote is called and Mr Obama would be nominated by acclamation under a deal between the two camps.
An opinion poll showed how much work remains for Mr Obama. A CNN/Opinion Research Corporation poll said he and Mr McCain were running even at 47 per cent - but only 66 per cent of Clinton supporters backed Mr Obama, down from 75 per cent at the end of June.
Twenty-seven percent of Clinton supporters said they would support Mr McCain, up from 16 percent in late June.