Hillary Clinton last night acknowledged for the first time that she may fail to halt Barack Obama's gathering momentum in the Democratic presidential race, saying: "Whatever happens - we’re going to be fine."

Her emotional comments in the final seconds of a TV debate with Mr Obama came after she was booed for resurrecting a plagiarism row, referring to a "Xerox" speech made by the Illinois senator.

New polls published today suggest she is in a tight - too close to call - fight for Texas and that her lead in Ohio has narrowed significantly, contests on March 4 that she needs to score victories in to keep her White House hopes alive.

During the debate last night Mrs Clinton succeeded in making the sort of emotional connection which has largely been lacking from her campaign for much of the past year.

Asked about she dealt with crisis, Mrs Clinton responded by alluding to the sexually stained scandals of Bill Clinton's White House. "I think everybody here knows I've lived through some crises and some challenging moments in my life."

Reaching out to shake her rival's hand, Mrs Clinton then continued: "No matter what happens in this contest - and I am honoured to be here with Barack Obama - we're going to be fine. You know, we have strong support from our families and our friends. I just hope that we'll be able to say the same thing about the American people, and that's what this election should be about."

Her remarks electrified the audience and provided a moment of genuine drama in a debate where both candidates had scored points without landing a knock-out blow. Mr Obama, by contrast, had answered the same question by giving a stock response about his self-chronicled life story.

But his aides later pointed out that part of Mrs Clinton's answer - where she said that despite "all of the challenges that I've had, they are nothing compared to what I see happening in the lives of Americans every single day" - appeared to have been lifted from Mr Clinton's campaign back in 1992.

David Axelrod, Mr Obama's chief strategist, said: "It was a good line then and it is a good line now. I don't begrudge her that - but we find it a little bit bewildering."

His avowed confusion was a reference to the past week in which Mrs Clinton's campaign had repeatedly accused Mr Obama of plagiarism for copying lines from his close friend and supporter, Deval Patrick, the Massachusetts governor.

The controversy had provided Mr Obama with his best moment in the debate. "The notion that I had plagiarised from somebody who was one of my national co-chairs, who gave me the line and suggested that I use it, I think, is silly," he said. "This is where we start getting into silly season, in politics, and I think people start getting discouraged."

Mrs Clinton had said: "I think that if your candidacy is going to be about words, then they should be your own words. That is, I think, a very simple proposition. And, you know, lifting whole passages from someone else's speeches is not change you can believe in, it's change you can Xerox." It was a remark that prompted boos from sections of the audience at Texas State University in Austin last night.

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