After primaries and caucuses in 42 of the 50 states, Obama leads his rival in convention delegates, popular votes and states won. She is struggling to stop his drive on the nomination by appealing to party leaders who will attend the convention as superdelegates that he will preside over an electoral defeat at a moment of great opportunity after eight years of Republican rule.
The former first lady has never denied published reports that she once told New Mexico Gov. Bill Richardson that Obama couldn't win when he called to tell her he would be endorsing the Illinois senator.
And at a news conference earlier this month in California, Clinton sidestepped when asked directly whether Obama would win if he were the Democratic nominee. "I am sure we will have a united Democratic Party. I will do everything possible to make sure we can win and I am confident we will have a Democrat in the White House next year," she said at the time.
Asked a similar question at the debate, she provided a similar answer at first. "I think we have to beat John McCain and I have every reason to believe we're going to have a Democratic president and it's going to be Barack or me."
Pressed by George Stephanopoulos of ABC News to answer the question directly, she said, "Yes, yes, yes ... Now I think I can do a better job."
In a debate that moved swiftly between politics and policy, Clinton issued a first-ever public apology for having claimed erroneously that she landed in Bosnia under sniper fire in 1996 as first lady.
"I may be a lot of things but I am not dumb," she said, adding that she had written in her book that there had been no gunfire during the episode. She said she was embarrassed by her error. "I'm sorry I said it," she added.
She previously had explained her incorrect comments by saying she had misspoken.
Obama later erred by saying he had never favored a ban on handguns even though as a state Senate candidate in 1996 he filled out a questionnaire from an Illinois voter group saying he would support such a ban.
"My writing wasn't on that particular questionnaire ... as I said, I have never favored an all-out ban on handguns," Obama said, even though his handwritten notes did appear on its front page. The reponse to the question about guns was typed.
Obama had more explaining to do moments later, when he was asked about his controversial comment that small town Americans become bitter because of economic adversity, and "cling to guns or religion or antipathy to people who aren't like them" as a result.
He said he was attempting to say that because voters feel ignored by government, "they end up being much more concerned about votes around things like guns where traditions have been passed on from generation to generation. And those are incredibly important to them."
"People don't cling to their traditions on hunting and guns" out of frustration with their government, Clinton said. She added that Obama had a fundamental misunderstanding on the role of religion and faith.