TOLEDO, Ohio (AP):

Hillary Rodham Clinton suggested she will press on following today's crucial primaries, arguing that momentum was on her side despite 11 straight losses to rival Barack Obama that have imperilled her Democratic presidential nomination bid.

Four states vote today, but the focus is on races in the big states of Texas and Ohio. The former first lady desperately needs wins in both states to salvage her once-powerful bid to become the US's first female president.

"I'm just getting warmed up," Clinton told reporters on Monday, looking ahead to a busy day of campaign events in Ohio and Texas where polls show a close race. Her husband, former President Bill Clinton, has asserted that his wife must win both states to keep her campaign alive.

A total of 370 delegates are at state in the four races, including Vermont and Rhode Island.

The key to winning

"Ohio is the key to winning the presidency, and I'm excited about tomorrow and I'm looking forward to it," she said, predicting success and looking to the next major primary in Pennsylvania on April 22.

A series of polls over the weekend has shown Clinton maintaining her lead in Ohio, even though Obama has narrowed the gap. Some polls showed Clinton with a slim lead; others with an advantage of up to 12 percentage points.

Obama has recently said that he is not ready to write the obituary for Clinton's White House bid yet. But on Monday, in an apparent sign of his confidence, the first-term senator said his rival may have no choice but to withdraw from the race if he does well in Ohio and Texas.

"If we do well in Texas and Ohio, I think the math is such where it's going to be hard for her to win the nomination," Obama said in an interview on ABC's Good Morning America new morning show. "And they'll have to make a decision about how much longer they want to pursue it."

'Buyer's remorse'

Clinton, who has bombarded Obama with criticism over his national security and foreign policy experience, has argued that failure by the first-term senator to win the four contests would signify a measure of "buyer's remorse".

Obama's aides said privately that they felt they had a good shot at a win in Texas, but were less certain about Ohio. Polls show Clinton leading in Rhode Island, but Obama ahead in Vermont.

Obama, who is seeking to become the US first black president, has spent the past days fending off attacks by Clinton.

"What precise foreign-policy experience is she claiming that makes her qualified to answer that telephone call at 3 a.m. in the morning?" Obama asked of Clinton at a town-hall meeting in Westerville, Ohio. It was a reference to duelling television ads over who would exercise superior judgement in responding to a national emergency in the middle of the night.