ABC News' George Stephanopoulos Reports: Sen. Hillary Clinton, D-N.Y., and former President Bill Clinton are making very direct arguments to Democratic superdelegates, starkly insisting Sen. Barack Obama, D-Ill., cannot win a general election against presumptive Republican nominee, Sen. John McCain, R-Ariz. Sources with direct knowledge of the conversation between Sen. Clinton and Gov. Bill Richardson, D-N.M., prior to the Governor's endorsement of Obama say she told him flatly, "He cannot win, Bill. He cannot win."Richardson, who served in President Clinton's cabinet, disagreed.At a rally in Oregon, standing next to Obama, Richardson insisted, "My great affection and admiration for Hillary Clinton and President Bill Clinton will never waver." But he added, "It is time, however, for Democrats to stop fighting among ourselves and to prepare for the tough fight we will face against John McCain in the fall."Yet here's a wrinkle, from a source with direct knowledge of Richardson's conversations with the Clintons: Richardson himself told Sen. Clinton and former President Clinton that he didn't think Obama could win, back when he was (according to the Clintons) telling them earlier this year that he wouldn't endorse Obama. "Too inexperienced," Richardson said, the source tells ABC News. WATCH GEORGE'S FULL WORLD NEWS REPORT BY CLICKING HERE.A report in the San Francisco Chronicle detailed another explosive exchange in which the former president angrily objected to Richardson's endorsement."Five times to my face [Richardson] said that he would never do that," Clinton said, according to the Chronicle -- before, the newspaper reports, he "went on a tirade that ran from the media's unfair treatment of Hillary to questions about the fairness of the votes in state caucuses that voted for Obama. It ended with him asking delegates to imagine what the reaction would be if Obama was trailing by just 1 percent and people were telling him to drop out."Another, neutral superdelegate who was in the room for that meeting called the Chronicle's take "a bit exaggerated." But there is no question the Clintons are passionately arguing their case against Obama in what is fast becoming an intense race not just for the votes of the public but of the Democratic elite known as superdelegates.For all the latest from the campaign trail, read The Note every day exclusively on ABCNews.com. And don't miss "The Last Lecture: A Love Story for Your Life", an unforgettable special about Professor Randy Pausch's inspiring last lecture at Carnegie Mellon about living life to the fullest, only on ABC.