Democratic and Republican presidential candidates have been crisscrossing the country in the final, fevered hours of campaigning before tomorrow's Super Tuesday, as polls show Hillary Clinton's lead over Barack Obama evaporating while John McCain surges ahead of Mitt Romney.
With more than 20 states in play tomorrow, including California and New York, candidates in both parties have been sharpening their closing arguments as they seek to motivate supporters to vote.
A Reuters/Zogby poll released yesterday shows Mr Obama within four points of Mrs Clinton nationally and ahead of her in California with the candidates virtually tied in New Jersey and Missouri.
Mr Obama's surge has been especially dramatic in California, the biggest prize tomorrow with almost a quarter of the delegates and a state where Mrs Clinton has had a clear lead for months.
The Reuters poll gives Mr Obama a slight lead over Mrs Clinton in the state, with 45 per cent to her 41 per cent, compared with a 17-point advantage she enjoyed only two weeks ago.
Mrs Clinton spent much of last week campaigning in California and Oprah Winfrey was due to hold a rally for Mr Obama in Los Angeles yesterday, appearing with his wife Michelle and Caroline Kennedy, daughter of the late president.
Both Democrats appeared on yesterday's political talk shows, arguing their case as the candidate with the best chance of winning the general election next November.
"I have been through these Republican attacks over and over and over again and I believe that I've demonstrated that, much to the dismay of the Republicans, I not only can survive, but thrive," Mrs Clinton said on ABC's This Week.
On Saturday, the candidates took part in a forum for young voters hosted by MTV, during which Mr Obama said his experience as a schoolboy in Indonesia would help him to change the perception of the US throughout the world. "If I convene a meeting of Muslim leaders to try to bridge the divide between Islam and the West, I do so with the credibility of someone who lived in a Muslim country for four years when I was a child. And although I'm a Christian I have a sense of that culture," he said.
Mr McCain told reporters in Nashville that he expected the Republican contest to end after tomorrow's primaries and caucuses and that he was confident of victory. "I assume that I will get the nomination of the party. I assume unifying our party is a very critical item and I believe we can do that and get everybody together and working together. And I'm confident I can do that," he said.
The Arizona senator is unpopular among many conservatives on account of his support for campaign finance reform, tougher action to combat global warming and comprehensive immigration reform. He has vaulted into a two-to-one lead over Mr Romney in recent days, however, benefiting from the withdrawal last week of former New York mayor Rudy Giuliani.
Most Republican contests tomor- row are "winner takes all" so the candidate with the most votes will claim all of a state's delegates. Democrats, however, use a form of proportional representation that divides delegates among the candidates, making it unlikely that a clear winner will emerge.
Complex rules mean that, in many congressional districts, Democratic delegates will be divided equally unless one candidate wins more than 60 per cent of the vote, a formidable hurdle in such a closely fought race.
Mr Obama enjoys a huge lead among African-Americans and young voters but Mrs Clinton is far ahead among women and Latino voters. Neither campaign believes that the Democratic race will be determined tomorrow and most expect it to continue at least until Ohio votes a month from now.