Mr Obama is expected to speak to Mr Clinton for the first time since he won the nomination in the next few days, but campaign insiders say that the former president’s future campaign role is a “sticking point” in peace talks with Mrs Clinton’s aides.
The Telegraph has learned that the former president’s rage is still so great that even loyal allies are shocked by his patronising attitude to Mr Obama, and believe that he risks damaging his own reputation by his intransigence.
A senior Democrat who worked for Mr Clinton has revealed that he recently told friends Mr Obama could “kiss my ass” in return for his support.
A second source said that the former president has kept his distance because he still does not believe Mr Obama can win the election.
Mr Clinton last week issued a tepid statement, through a spokesman, in which he said he “is obviously committed to doing whatever he can and is asked to do to ensure Senator Obama is the next president of the United States “.
Mr Obama was more effusive at his unity event with Mrs Clinton on Friday, speaking fondly of the absent former president, who attended Nelson Mandela’s birthday celebrations in London instead. The candidate told the crowd: “I know how much we need both Bill and Hillary Clinton as a party. They have done so much great work. We need them badly.”
But his aides said he has so far concentrated on cementing relations with Mrs Clinton first. They say they are content to let relations with Mr Clinton thaw gradually.
It has long been known that Mr Clinton is angry at the way his own reputation was tarnished during the primary battle when several of his comments were interpreted as racist.
But his lingering fury has shocked his friends. The Democrat told the Telegraph: “He’s been angry for a while. But everyone thought he would get over it. He hasn’t. I’ve spoken to a couple of people who he’s been in contact with and he is mad as hell.
“He’s saying he’s not going to reach out, that Obama has to come to him. One person told me that Bill said Obama would have to quote kiss my ass close quote, if he wants his support.
“You can’t talk like that about Obama – he’s the nominee of your party, not some house boy you can order around.
“Hillary’s just getting on with it and so should Bill.”
Another Democrat said that despite polls showing Mr Obama with a healthy lead over Republican John McCain, Mr Clinton doesn’t think he can win.
The party strategist, who was allied to one of the early rivals to Mr Obama and the former First Lady, said Mr Clinton was “very unhopeful” about the nominee’s prospects in November.
“Bill Clinton knows the party will unite behind Obama, but he is telling people he doesn’t believe Obama can win round voting groups, especially working-class whites, in the swing states,” the strategist said.
“He just doesn’t think Obama will be able to connect with the voters he needs.”
Joe Klein, the author of Primary Colours, a fictionalised account of Mr Clinton’s 1992 election, who has known the former president for 20 years, said he also heard that he was “very, very bitter”, from people who have spoken with him.
“It’s time for him to get over it or go off and do his charitable work. He knows the rules of the road. What’s going on now is kind of strange. I think his behaviour is really, really shocking.”