Mr. Obama accused Mrs. Clinton of saying anything to get elected. On Sunday he had accused her husband Bill Clinton of making false statements about him. But Mrs. Clinton said it was hard to debate with someone who never took responsibility for any vote he cast. A third candidate, John Edwards, accused them of squabbling. The three candidates also debated the economy and racial justice, with attacks on President George W Bush's plan to stave off recession. Mr. Obama needs to win Saturday's South Carolina primary to re-invigorate his campaign after successive defeats to the former first lady in New Hampshire and Nevada. The debate marked a significant gear-shift with just two weeks before "Super Tuesday", when 22 states vote in a potentially decisive day for the party's nomination contest.

Heated exchanges

John Edwards

Monday's often acrimonious debate saw heated exchanges in which the Illinois senator told Mrs. Clinton that he was helping unemployed workers on the streets of Chicago when "you were a corporate lawyer sitting on the board at Wal-Mart". The New York senator retorted that she was fighting against misguided Republican policies "when you were practicing law and representing your contributor ... in his slum landlord business in inner city Chicago", a reference to Antoin Tony Rezko, who is facing charges for fraud. Mr. Obama's campaign has given to charity the funds which it has received from donors linked to Mr. Rezko. With Monday marking a national holiday to honor the slain civil rights leader Martin Luther King, and more than half of South Carolina's voters being black, racial equality was also addressed. Trailing the two front-runners by a wide margin, Mr. Edwards attempted to rise above the acrimony while pleading for an equal hearing. "Are there three people in this debate, not two?" asked the former North Carolina senator. "We have got to understand, this is not about us personally. It's about what we are trying to do for this country." The Republican presidential contenders, meanwhile, were focusing their attention on Florida ahead of the state's primary on 29 January.
 

Democratic Senator Hillary Clinton has defeated Barack Obama in the Nevada caucuses, while former Massachusetts governor Mitt Romney won the Republican contest with little opposition. Our US West Coast correspondent David Willis reports.

Hillary Clinton's victory in Nevada has re-established her place as the Democratic front-runner and the candidate to beat. The New York senator's second victory in a row makes up for her poor showing in the Iowa caucuses; it also marks a departure from the white, homogenous voter base of both Iowa and New Hampshire. Nearly a quarter of Nevada's population is Hispanic, and many, it seems, prefer Hillary Clinton to Barack Obama. The Clinton campaign was dealt a set-back when Senator Obama gained the endorsement of the biggest and best-organized union in Nevada - the Culinary Workers' Union.

Clinton supporters went to court in an attempt to halt the use of so-called 'special precincts' - designed to help casino employees caucus along the famous Las Vegas strip - claiming this dealt an unfair advantage to their rival. They failed to gain the judge's backing, but seemed to have no issue with the result. Mrs Clinton called it a "huge victory" and said it underlined the "broad base" of her support. There was additional controversy over a television advert on Spanish language channels in which supporters of Mr Obama called Mrs Clinton "shameless". Nevertheless a spokesman for the Obama campaign said their candidate fought "an honest campaign" and accused the Clinton camp of attempting to mislead caucus-goers by making "false and divisive attacks".

Black voters

Monday sees the next Democratic debate ahead of the party's South Carolina primary on 26 January. The debate takes place in Myrtle Beach, South Carolina. Fittingly perhaps - given that that is Martin Luther King Day - the event is sponsored by the Congressional Black Caucus. The debate could prove an apt curtain-raiser to the vote in South Carolina, where race issues of a different kind will take centre stage.

Almost a third of the population in the state is African-American and South Carolina will therefore be the first Democratic primary in which black voters will play a crucial role in the outcome. Senator Obama needs a victory there to counter his defeats in Nevada and New Hampshire. The polls suggest he currently enjoys a slight lead in the state, but there is still all to play for. In Nevada's Republican race Mitt Romney recorded his third victory in a row, although the free-spending candidate was one of very few from his party to actually campaign there.

The Republican result is non-binding, which means delegates are not obliged to stick with their decision at the election itself. Nonetheless, just like Hillary Clinton, Mr. Romney may find that victory there will add to his momentum in the run-up to the all-important Super Tuesday ballot. For her part, Mrs. Clinton will be particularly pleased with the support she has gained from Hispanic voters, who make up a considerable proportion of voters in the Super Tuesday contests, not least in New York and the most populous state in the union, California.