"There are going to be some of Sen. Clinton's supporters who we're going to have to work hard to persuade to come onboard," he said. "That's not surprising. 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."
Friends of Bill Clinton, however, say he is still angry at Obama for waging a campaign that often criticized the accomplishments of the Clinton years. They say he's also unnerved that Obama allies accused him and his wife of trying to tag Obama as "the black candidate," as on the day of the South Carolina primary when he compared Obama to Jesse Jackson, saying, "He ran a good campaign here. Jesse Jackson ran a good campaign too." Obama backers have also suggested that Hillary Clinton was trying to disrespect Martin Luther King Jr. when she argued that it took President Lyndon Johnson, a lawmaker not just an orator, to make King's dream a reality.
Bill Clinton does not believe he said or did anything wrong.
"For any innuendo to suggest ... that Clinton was raising the race card ... still angers him, and justifiably so," said Lanny Davis, a former Clinton White House official and close friend of the Clintons.
Rep. Jim Clyburn was offended, and told Bill Clinton as much in a phone call around that time.
"I've always described the conversation as being less than pleasant," Clyburn said.
Davis said, "Congressman Clyburn, who before the South Carolina primary, warned President Clinton about ... 'getting too close to the line,' owes him an apology. Everybody who criticized Sen. Clinton, not Barack Obama, after she made her remark about MLK and LBJ, especially leaders of the black community who I heard criticize her, owe her an apology."
Another source of tension involves perceived sexism Clinton and her supporters say they observed in the media. On Monday, Clinton supporters directed their anger toward MSNBC "Hardball" host Chris Matthews, chanting "Sexist pig, sexist pig."
Matthews issued an on-air apology in January after making a comment during a guest appearance on Joe Scarborough's MSNBC show "Morning Joe." While on the program Matthews said, "The reason she may be a front-runner is her husband messed around," referring to Clinton's success in the New Hampshire presidential primary.
"Was it fair to imply that Hillary's whole career depended on being a victim of an unfaithful husband? No," said Matthews on "Hardball." "And that's what it sounded like I was saying, and it hurt people who I'd like to think normally like what I say; in fact, like me."
There has also been lingering resentment between the two camps abut post-primary issues -- the Clinton team thinks Obama has not been helpful enough in helping Clinton retire her more than $30 million in debt, believing Obama has been arrogant and rude
The Obama campaign would like the Clintons to acknowledge his win with some deference and grace.
Tonight on NY1, a New York cable news channel, Clinton's former campaign chairman Terry McAuliffe told the Obama team, "You're nominated to be president. It's your campaign. At some point, quit talking about the Clintons and move on."
That would likely be easier if the Clintons and their supporters stopped talking about the Clintons and moved on, too.
ABC News' Deborah Apton contributed to this report.