As the Democratic candidates hunker down for a war of attrition, aides to Hillary Clinton revealed that she dipped into her personal fortune last month to lend the campaign $5 million.

This signals what many would have considered unthinkable three months ago - the potential financial vulnerability of her bid.

The Clinton campaign also disclosed that several senior staffers, including her campaign manager, are voluntarily working without pay.

The New York senator (seen above on February 5) made the loan in late January during the run-up to Super Tuesday, in which she and Barack Obama fought to a virtual draw in a quasi-national primary.

Both campaigns are still arguing the number of delegates won.

During January, Obama raised a staggering $32 million to $13.5 million for Clinton and expanded his donor base to more than 650,000.

Unlike the Clinton campaign, which depends heavily on wealthy contributors who have already reached the $2,300 legal limit they can give, Obama raised that from smaller donors - ones who can keep giving.

“Heading into the next states, Barack Obama has a clear money advantage,” said CNN analyst Gloria Borger said.

“Now Hillary Clinton wants to debate every single week because she doesn’t have the money to compete with him for paid media. I think we’ll be seeing a lot more Obama and Hillary Clinton one-on-one.”

Next up? The Louisiana primary, Nebraska and Washington caucuses Saturday, Maine caucuses Sunday, and the so-called “Potomac primaries” or “Beltway primaries” in Virginia, Maryland and D.C. Tuesday.