Edwards and his wife, Elizabeth, have remained studiously neutral since the Edwards campaign came to a close Jan. 30. Edwards on Sunday called Obama "the likely nominee," but made clear that his statement reflected a judgment about the state of the race, not necessarily a personal preference.
The possibility of an Edwards endorsement has been the subject of intense speculation for months; only former vice president Al Gore's endorsement was more coveted by Obama and Clinton. Edwards and his wife had publicly praised Clinton's healthcare plan, but Edwards' anti-corporate message seemed a better fit for Obama's outsider campaign.
Edwards, who received a thunderous ovation when Obama introduced him to a crowd of several thousand, said, "brothers and sisters, we must come together as Democrats" to defeat McCain. "We are here tonight because the Democratic voters have made their choice, and so have I."
He said Obama "stands with me" in a fight to cut poverty in half within 10 years.
Edwards also praised Clinton, saying "we are a stronger party" because of her involvement, and "we're going to have a stronger nominee in the fall because of her work."
He said Clinton is a "woman who is made of steel. She is a leader in this country not because of her husband but because of what she has done."
A source close to the Clinton campaign said the Edwards camp gave the Clinton folks a head's up.
"Clearly it's upsetting" the source tells ABC. "He brings the workers" to Obama.
"Well I don't think it's good news, but there's a lot of news in this business and we move forward and move past it," a senior Clinton advisor told ABCNews. "It's not great news."
Asked what effect the Edwards endorsement might have, he said: "We don't know. We'll see. We'll see how much of it is transferable," referring to Edwards' popularity with white working class voters.
"We would've preferred it" to be our endorsement, the advisor said. "That's not a secret."
Clinton met today with six uncommitted superdelegates at the DCCC offices on Capitol Hill.
This advisor said the Clinton campaign believes superdelegates are concerned about Obama's loss in West Virginia last night and other swing states.
"No question - that started with Ohio and increased with Pennsylvania, Indiana and West Virginia...All I can say is, I don't want to overdramatize it, but starting with Ohio, the remaining superdelegates started really focusing on the 270 electoral vote issue and how do we best assemble that, and it's made a marked impression."
But then, in a moment of candor, the advisor conceded, "I'm not sure it's gonna be enough."