The former presidential candidate George McGovern increased pressure on the Clinton campaign tonight by ending his support for the New York senator and urging her to drop out of the race for the Democratic nomination.

The latest blow to Mrs Clinton’s faltering bid came as she loaned her own campaign another $6.4 million in a desperate attempt to maintain her presidential challenge.

Senator McGovern had been a high profile Hillary Clinton supporter but today he insisted that she had virtually no chance of winning. The 1972 Democratic presidential nominee said he was endorsing Senator Barack Obama after studying the returns from the North Carolina and Indiana primaries.

“I will hold them in affection and admiration all of my days,” he said of the Clintons, close friends from his early political career.

“She has run a valiant campaign. Hillary, of course, will make the decision as to if and when she ends her campaign. But I hope that she reaches that decision soon so that we can concentrate on a unified party capable of winning the White House next November."

Mr Obama’s comfortable win in North Carolina and Mrs Clinton’s narrow victory in Indiana have left the Illinois senator in a commanding position with just six contests left before the Democratic Convention.

And the Clinton campaign admitted today that the candidate had been forced to put her hand in her own pocket to keep the campaign running after a sharp drop in donations.

In the past month she has leant the campaign $6.4 million, including $1.4 million in the past week - the second time she has dipped into her personal fortune to fund her presidential bid.

“She did this in order to remain competitive with Senator Obama on television,” said Howard Wolfson, a Clinton spokesman.

“The loans are a sign of Senator Clinton’s commitment to the race, commitment to continuing the process and a commitment to being competitive with Senator Obama.”

Mr Wolfson and other aides denied suggestions that this week's results doomed Mrs Clinton to eventual defeat.

“The reality is that many pundits have counted Senator Clinton out many times during this contest,” Mr Wolfson said. “We believe ultimately that voters are more important than pundits.”

The next round of voting will come in West Virginia next Tuesday. The following week it is the turn of Oregon and Kentucky. There are six contests remaining, leaving it very difficult for Mrs Clinton to secure enough votes to sway the Convention in her favour.

“We have seen that it’s possible to overcome the politics of division and distraction, that it’s possible to overcome the same old negative attacks that are always about scoring points and never about solving our problems,” Mr Obama said at a victory rally in Raleigh, North Carolina.

His 14-point victory in the state was a dramatic comeback from a difficult campaign stretch that began last month with a big loss in Pennsylvania, and was prolonged by the controversy over racially charged comments by his former pastor, the Reverend Jeremiah Wright.

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