US:Democratic presidential hopefuls Barack Obama and Hillary Clinton will debate in Texas tonight as Mrs Clinton struggles to keep her candidacy viable after two crushing defeats on Tuesday.
Mr Obama won Wisconsin by 17 points and in Hawaii, where he was born, he defeated Mrs Clinton by a margin of three to one.
The former first lady, who has lost all 10 Democratic primaries and caucuses since Super Tuesday, is depending on victories in Texas and Ohio on March 4th to halt Mr Obama's gathering momentum. She told supporters in New York yesterday that while Mr Obama was running "a campaign about a campaign", she was the more effective champion of ordinary Americans. "It's time to get real about how we actually win this election," she said. "It's time that we move from good words to good works, from sound bites to sound solutions."
Mr Obama's victory in Wisconsin was a severe blow to Mrs Clinton, not least because he was the choice of almost every demographic group, including white men and lower-income voters.
Mrs Clinton was ahead among voters over-65, Catholics and those without a college education, but Mr Obama has expanded his coalition far beyond its core of the affluent, the well-educated and African-Americans.
The breadth of Mr Obama's support in Wisconsin is especially worrying for Mrs Clinton as she turns her attention to Ohio, which has a similar mix of voters. Mrs Clinton is still ahead in the polls in Ohio, but Mr Obama has closed in upon her in Texas, where voters will participate in both a primary and a caucus on March 4th.
One third of the state's delegates will be chosen in the caucus, a format in which Mr Obama has usually out-performed his rival.
Addressing almost 20,000 people in Houston on Tuesday night, Mr Obama warned that the race for the Democratic nomination was not yet over.
"The change we seek is still months and miles away and we need the good people of Texas to help us get there," he said.
He now enjoys a lead of about 150 among pledged delegates, so Mrs Clinton would have to win more than 65 per cent of the votes in Texas and Ohio to draw level with him.
Her string of defeats has unnerved supporters and some super-delegates - senior party figures who account for one-fifth of the votes at the nominating convention in August - have already abandoned her.
Mr Obama's campaign is more lavishly funded and better organised and Mrs Clinton's advisers have been bickering in recent days about how best to salvage her candidacy. Some senior advisers believe that she must step up her attacks on Mr Obama in the hope that he will stumble during the next few weeks. Others fear that negative campaigning will depress Mrs Clinton's support even further, widening the delegate gap with Mr Obama.
Privately, Mrs Clinton's staff believe that, although Mr Obama has run a remarkable campaign, he is a vulnerable candidate who has yet to be tested by hostile media attention or Republican attacks. They hope that if Mrs Clinton can remain in the race long enough - at least until after Pennsylvania votes on April 22nd - voters will begin to experience "buyer's remorse" about her rival.
Mr Obama's front-runner status was confirmed on Tuesday when the likely Republican nominee, John McCain, used a victory speech after the Wisconsin primary to make a thinly veiled attack on the Illinois senator.
"I will fight every moment of every day in this campaign to make sure Americans are not deceived by an eloquent but empty call for change - no more than an eloquent but empty call for change that promises no more than a holiday from history and return to the false promises and failed policies of a tired philosophy that trusts in government more than the people," Mr McCain said.
Earlier, Mr McCain's wife Cindy waded into a row over Michelle Obama's statement on Monday that "for the first time in my adult lifetime, I am really proud of my country".
Introducing her husband at a campaign event, Mrs McCain shared her own patriotic feelings. "I'm proud of my country," she said. "I don't know about you, if you heard those words earlier, I'm very proud of my country."
Mr McCain defeated former Arkansas governor Mike Huckabee by 22 points, putting the Arizona senator within reach of the 1,191 delegates he needs to secure the nomination.
Mr McCain could cross that hurdle on March 4th if he wins Texas and Ohio, but Mr Huckabee remains adamant that he will stay in the race until it is over, dismissing claims that he is on an ego-trip.
"Let me assure you that if it were ego, my ego doesn't enjoy getting these kinds of evenings when we don't win the primary elections," he said.
"It's got to be something other than that, and it is. It's about convictions, it's about principles I dearly, dearly believe in."