Hillary puts her faith in Texas and Ohio to retain hope of nomination

With her back to the wall, nobody doubts that Hillary Clinton will put up a tenacious fight to derail the Obama bandwagon which is picking up momentum. The only question is how nasty a struggle it becomes and how much ammunition she hands to the Republicans in the process.

As news of her defeats in Virginia, Maryland and Washington DC sank in, Mrs Clinton was as far away as possible, courting Hispanic voters in El Paso, Texas. She did not mention Tuesday's defeat, even as the wheels started coming off her campaign. Mrs Clinton's deputy campaign manager Mike Henry, who ran her field operations, quit in an internal power struggle.

But by yesterday morning, her campaign was on the offensive, demanding Barack Obama engage in more televised debates and accusing him of misrepresenting her positions.

Part of Mrs Clinton's strategy is to build a "firewall" in the Ohio and Texas primaries on 4 March, to hold back the prairie fire of enthusiasm driving Mr Obama forward. But staking everything on one or two important races is a very high-risk strategy, one which failed Rudy Giuliani in Florida, forcing him out of the Republican race.

In her desperate attempt to wrest the Democratic ticket for the White House from Mr Obama, well-heeled backers of Mrs Clinton are now expected to turn to the dark arts of the political playbook, including discrediting her opponent. It would be a role reversal for Mrs Clinton who once complained that there was "a vast right-wing conspiracy" out to get her.

But if the fight turns ugly, Mrs Clinton could end up wrecking both her and Mr Obama's chances of winning the White House in November. The Clinton campaign has already suffered badly by trying to raise the issue of Mr Obama's use of cocaine as a youth and then attempting to use the race card against him before and during the South Carolina primary. But more is now expected and the Obama campaign has said all along that there will be a lot of turbulence before it clinches the nomination.

Mrs Clinton's latest strategy could be to discreetly encourage independent organisations to fight on her behalf – a variation of the "Swift Boat" campaign that helped destroy John Kerry and win George Bush a second term in 2004. Some of her wealthiest backers are drawing up plans to skirt around election laws and run their own independent advertising campaigns attacking Mr Obama ahead of the primary battles in Ohio, Texas and elsewhere.

Susie Tompkins Buell, the founder of the Esprit clothing company, is considering paying for advertisements that would deliver a harder punch than the bland, uplifting advertisements the Clinton campaign is running. "We're just trying to figure out things to do to help," Ms. Buell told The Wall Street Journal. "We all feel very passionate about it, so the question is, what is the best thing we can do to get her across the finish line?"

Mrs Clinton and her staff are forbidden by law from talking to anyone running an independent campaign on her behalf. But in an extended television interview on the eve of her defeat in the "Potomac Primaries" she did the spadework for anyone contemplating running "attack ads" on her behalf. "We still don't have a lot of answers about Senator Obama and his dealings with Mr [Tony] Rezko," she said referring to a former political backer who is facing trial on federal corruption charges.

The danger for Mrs Clinton is that attack ads by independent organisations could backfire. Mr Kerry has already warned against the sort of tactics employed by the "Swift Boat Veterans for Truth" group that questioned his record in Vietnam.

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