Barack Obama wins Wisconsin primary
The Hawaii caucuses were expected to make her a 10-time loser in the 14 days since Super Tuesday, raising the stakes for Clinton to rebound with victories in Texas and Ohio on March 4 or face the collapse of her White House ambitions.
Obama already leads in total delegates - an advantage that will grow with Tuesday's vote.
Exit polls in Wisconsin suggested Obama continued to chip away at the Clinton base that once made her camp confident of winning the Democratic nomination, fueling doubts about whether her must-win strategy in Ohio and Texas is attainable.
In beating her handily, Obama edged Clinton among white voters, tied her among women, including white women, and made significant headway among families with incomes under $50,000.
Among independents, a pivotal group in the general election, Obama beat her, 63% to 34%.
Clinton and her aides steeled themselves for a fierce, two-week battle for Texas and Ohio, two of the largest states remaining on the calendar. If she loses them, even close supporters predict she will be toast.
Speaking in Ohio Tuesday night, Clinton made clear she won't go down without a fight.
"Both Sen. Obama and I would make history," Clinton said. "But only one of us is ready on day one to be commander in chief, ready to manage our economy, and ready to defeat the Republicans. Only one of us has spent 35 years being a doer, a fighter and a champion for those who need a voice."
But in a sign of Clinton's second-class standing in the race, cable television networks abruptly cut away from her remarks when Obama began addressing a cheering Texas crowd.
"Houston, I think we've achieved liftoff here," he quipped.
Obama was a favorite to win Hawaii, his native state, when results come in Wednesday morning.
Clinton aides, who can't survive on settling low expectations much longer, boasted Tuesday they'll eat Obama's lunch in Texas by taking the youth vote and dominating among Latinos.
David Plouffe, Obama's campaign manager, said he expected Team Clinton to run a "harshly negative" campaign in Texas and Ohio. The Clinton campaign launched its first negative ads of the season in Wisconsin.
"The change we seek is still months and miles away and we need the good people of Texas to help us get there," Obama told a Houston crowd estimated at more than 18,000 strong.