Hillary Clinton's struggle to keep her campaign alive is being made tougher by a drying up of donors, forcing her to lend herself $6.4m (£3.2m).
Her poor showing in Tuesday's primaries - losing badly in North Carolina and winning narrowly in Indiana - will make it even harder to attract donors for what many will regard as a doomed campaign.
She has been unable to compete with rival Barack Obama in terms of funding since last year and had to lend her campaign $5m in February. Although her campaign team claimed she raised $10m in 24 hours after winning Pennsylvania last month - sceptics are waiting to see the accounts - her campaign has been running with large debts.
Obama is well placed to seriously outspend her in the six remaining primaries.
Clinton's campaign today indicated that she intended to fight on even as her hopes of winning the Democratic presidential nomination dwindled.
However, in what could prove portentous for the race, former senator and presidential candidate George McGovern switched his allegiance today from Clinton to Obama and urged Clinton to drop out of the race.
After watching the returns from the North Carolina and Indiana primaries Tuesday night, McGovern said it's virtually impossible for Clinton to win the nomination. McGovern, a former South Dakota senator and 1972 Democratic presidential nominee, said he planned to call Bill Clinton to tell him of the decision and said he remains close friends with the Clintons.
She failed to close the gap on Obama in two key primaries last night, winning Indiana by a slim margin - 51% to 49% - but seeing that outweighed by her rival's 56% to 42% landslide in North Carolina.
Indiana provided an exhilarating finish, with the outcome in doubt almost until the last vote was counted, six hours after polling closed.
Obama had prematurely conceded defeat and Clinton made a victory speech, but her margin continued to shrink as the votes kept coming in.
Clinton had needed to win both North Carolina and Indiana, the last two big states left in the contest, to stand a chance of reining in Obama.
But in a speech in Indianapolis last night, she gave no indication that she was ready to concede, saying: "It is full speed to the White House."
Clinton's schedule for today includes a rally in West Virginia, where voters head to the polls next week, and a fundraising event in Washington.
Tomorrow, events are planned in Oregon and South Dakota, which vote on May 20 and June 3.
But with only six primaries left, Obama is within touching distance of securing the Democratic nomination to face the Republican, John McCain, in November's general election.
Last night, Obama secured a bigger share of the delegates - who will choose the nominee - to add to his already commanding lead.
With 99% of the vote counted in Indiana, Clinton had 638,274 (51%) and Obama 615,862 (49%).
Mayor Rudy Clay, an Obama supporter from Gary, north-west Indiana - one of the last places to announce its results - denied there had been any "hanky-panky", but mayor Tom McDermott of Hammond, a Clinton supporter, said there was "a perception of impropriety".
There were no such doubts in North Carolina. With 99% of the vote counted, Obama won a sweeping 890,695 to Clinton's 657,920.
Given her failure to make a breakthrough last night, Clinton will struggle to raise money for the remainder of the campaign and made an appeal for funds.
She could, in theory, keep on fighting all the way to the Democratic party convention in Denver in August.
At an election night party in Raleigh, North Carolina, Obama looked beyond the primaries to the November contest with McCain.
He denounced political pundits who said his contest with Clinton had polarised the party and that Clinton's supporters would not turn out to support him in November.
In exit polls yesterday, one-third of Clinton backers claimed they would vote for McCain if he faced Obama in November. One in five Obama supporters said they would vote for McCain over Clinton.
"Yes, there have been bruised feelings on both sides. Yes, each side desperately wants their candidate to win," Obama said.
"This primary season may not be over, but when it is we will have to remember who we are as Democrats."
He predicted the party would unite behind him in the autumn, adding: "This fall, we intend to march forward as one Democratic party, united by a common vision for this country."
His call for unity was intended to reassure senior Democrats worried about his weakness in failing to finish off Clinton and his failure to connect with white working class voters.
Terry McAuliffe, Clinton's campaign manager, argued that Obama's defeat in Indiana - which borders his home state of Illinois - was a sign of weakness in his candidacy.
"He cannot beat us in these big industrial breadbasket states that you need to win in November, and that's a problem," McAuliffe said.
The breakdown of the vote again highlighted the extent to which the Obama-Clinton contest has divided along racial lines.
While Clinton now has very little support among African-Americans, the results demonstrated Obama's continued difficulties in attracting white voters.
Exit polls showed Clinton won 61% support among white women in Indiana and 58% among white men.
The racial divide was stark in North Carolina, where Obama took 91% of the African-American vote and Clinton only 6%. Around one-third of the Democratic vote in the state is African-American.
The two primaries came after Obama had been on the back foot for the last two months.
Opinion polls in North Carolina last week indicated that his 25% lead at the start of the campaign had withered to single digits.
Last week was his worst since he launched his campaign for the presidency last February.
He was tested by an incendiary public appearance last week by his former pastor, the Reverend Jeremiah Wright, which pushed race up the agenda.
Among voters polled yesterday, 48% of Democrats in Indiana and 48% in North Carolina said Wright's comments - portrayed in the US media as unpatriotic - were "very" or "somewhat" important to their vote.
White voters tended to say the issue was important, while African-Americans tended to say it was not.
Obama won at least 94 delegates in the North Carolina and Indiana primaries, according to an analysis of election returns by the Associated Press.
Clinton won at least 75 delegates, with 18 still to be awarded.
In the overall race for the nomination, Obama leads with 1,840 delegates, including separately chosen party and elected officials known as superdelegates. Clinton has 1,684. A total of 2,025 delegates is needed to clinch the nomination.
The six remaining primaries remain have only a relatively small number of delegates, 217.
In addition, there are 270 undecided Democratic superdelegates - Congress members and others with an automatic vote.
The populist strategy deployed by Clinton in Indiana and North Carolina will be crucial to her efforts to woo those superdelegates.
Her campaign argues that her success in winning over working class voters in Ohio, Pennsylvania and now Indiana makes her a stronger candidate than Obama against McCain, even though Obama has won the majority of Democratic contests.
In Indiana, the strategy saw Clinton ditching her previous persona of wordly first lady and policy wonk to reinvent herself as a tough, beer-loving heroine of the working classes.
The populist appeal was the most determined effort to date by Clinton to solidify her support among working class white men following her victories in Ohio and Pennsylvania.