With no realistic avenue available to the Democratic presidential nomination, the former first lady soldiered on yesterday, limping into West Virginia in what her admirers would call a remarkable display of resilience. Her detractors would call it a single-minded compulsion.

INDIANAPOLIS–If there is a fine line between gritty, feisty, underdog and quixotic campaigner in denial, Hillary Clinton may have crossed it yesterday.

She is broke and had to loan her campaign another $6.4 million to keep it afloat. George McGovern, who in 1972 was the first presidential candidate Clinton campaigned for, called on her to drop out.

But the clock is about to strike midnight for the once-inevitable nominee.

"It's still early," she said in Shepherdstown, W. Va.

The Clintons, including husband Bill, have always practised the politics of attrition, outlasting their adversaries, making it hard to see the writing on the wall.

Some politicians don't know how to lose, and that may be what is keeping Clinton on the campaign trail.

There's no shortage of theories because the inner workings of Hillary Clinton have always fascinated supporters and opponents alike.

To win, she must somehow convince 70 per cent of uncommitted superdelegates that she, and not the man she trails, Barack Obama, is more electable in November.

She may want to go out a winner, taking West Virginia next week and Kentucky on May 20 before bowing to the inevitable.

She can hope for the political equivalent of a lightning strike, some seismic stumble by Obama or some unforeseen scandal lurking under his bed.

Or, those around her say, it may be simply that in her heart she believes she would make a better president than Obama and she believes she deserves the shot at the White House, not him. It seems unlikely anyone, including Bill Clinton, can tell her when to get out.

"I'm staying in this race until there's a nominee," she said.

"And I obviously am going to work as hard as I can to become that nominee. That is what I've done. That's what I'm continuing to do."

At 2 a.m. yesterday, after learning that television pundits and newspaper websites had declared her dead following her razor-thin Indiana victory, she decided she had to appear at the West Virginia rally that was originally scheduled for daughter Chelsea.

In deference to the Clinton brand in the Democratic party, elders and superdelegates appeared content to let the New York senator see the race to its conclusion June 3, when superdelegates are then expected to quickly coalesce and confirm the nomination of Obama.

Their patience would end, however, if she is seen to be using these final weeks to try to damage Obama.

Her most recent loan includes money from Bill Clinton, and they have now poured $11.4 million of their own money into the campaign to keep it afloat.

The donor well may be drying up.

Unlike the morning after her win in Pennsylvania last month, when the campaign kept announcing ever-increasing fundraising totals, the campaign was silent on that front yesterday.

"As we've told each other time and time again, there will be good days and not so good days in the course of this campaign," she said in a fundraising appeal.

"But there will never be a day that we can't count on one another."

After his win in North Carolina, Obama has a lead of 172 among pledged delegates and needs only 33 more from clinching a majority of the earned delegates, something the campaign says will happen in Oregon on May 20.

Obama needs fewer than 200 delegates to clinch the nomination outright.

An Associated Press count shows he won at least 94 delegates Tuesday. Clinton won at least 79 delegates, with 14 still to be awarded. Including superdelegates, Obama had 1,840.5 delegates, Clinton had 1,688. The winner needs 2,025 delegates to clinch the nomination.

As well as getting McGovern on his side, Obama added four more superdelegates yesterday.

Obama also has an insurmountable 700,000 lead in the popular vote, not including Michigan and Florida, which held primaries but were stripped of their delegates for moving their primaries ahead of a party-designated date.

"We can see the finish line," said Obama campaign manager David Plouffe.

McGovern issued his call a day before Clinton was scheduled to campaign in his home state of South Dakota. But the Obama campaign will not make a similar call, said Missouri Senator Claire McCaskill, the campaign co-chair.

"As much as we believe in Barack Obama ... there is sincere respect for Hillary Clinton within this campaign," she said.

"It would be inappropriate, awkward and wrong for anyone in this campaign to tell Hillary Clinton to get out of the race."

The Obama campaign will be "appropriately deferential" to the strong campaign she has run, McCaskill said.

Terry McAuliffe, Clinton's campaign chair, pulled out every sports comeback he could think of – New York Giants' quarterback Eli Manning, boxer George Foreman, the seventh game of the World Series – to tell television interviewers she can still win.

"Nothing's impossible," he said.