Democrats Hillary Clinton and Barack Obama were locked in a near dead heat two days before the biggest presidential voting so far while John McCain tries to nail down the Republican nomination for the White House.
With 24 states holding nominating contests on Tuesday, the candidates spent their Sundays appearing on the morning television talk shows and campaigning across the country as polls showed the two races going in opposite directions.
The Democratic race, which Ms Clinton once led handily, had narrowed to a nearly a draw in recent national polls.
Mr Obama held a slight lead in California and was virtually tied with Ms Clinton in New Jersey and Missouri - three states voting on "Super Tuesday" - in a Reuters/C-SPAN/Zogbypoll released today.
While the two people seeking to be the Democratic choice were vying to win the most delegates needed for nomination, they also were making the argument of being the most electable candidate to face Mr McCain in the November election.
"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," Ms Clinton said on ABC's "This Week."
Ms Clinton, the New York senator who was a major target of conservatives while first lady during President Bill Clinton's terms in office, said her record was well known and she had already weathered heated attacks while Mr Obama, a first-term senator from Illinois, was still an unknown quantity.
"I think I can get some votes that Senator Clinton cannot get," Mr Obama, who would be the first black president, said on CBS's Face the Nation. "That broadens the political map. I think it bodes well for the election."
"I'm always pleased to have so much attention from the nominees -- or the two contenders for the Democratic nomination," Mr McCain said on CBS's Face the Nation.
Even with half the Democratic national convention delegates at stake and more than 40 per cent of the Republican, no candidate could clinch the nomination on Tuesday but a big vote across the board could go a long way toward that goal.
Mr McCain, an Arizona senator, held a 2-to-1 margin in a new national Washington Post-ABC poll. In the Reuters/C-SPAN/Zogby poll, Mr McCain held double-digit leads in New York, New Jersey and Missouri but narrowly trails former Massachusetts Govenor Mitt Romney in California, the biggest prize on "Super Tuesday."
In an effort to embarrass Mr Romney in the state he once served as governor, Mr McCain was in Massachusetts on Sunday to watch the local football team, the New England Patriots, play in the Super Bowl.
But even as his lead in the polls widened and a big win on Tuesday could sew up the nomination for him, Mr McCain still faced questions from one section of the party over whether he was conservative enough.
Mr Romney hit that theme and pointed to a large turnout in Maine on Saturday that gave him a victory there as evidence conservatives were giving Mr McCain another look.
But Mr McCain pointed to a number of prominent Republican conservatives who were supporting him.
"I'm very happy with where we are," he said. "I know that Tuesday is going to be hotly contested ... And I'm pleased at the gathering support from all parts of the party that we're gaining."
One of the problems facing Mr Romney on Super Tuesday is that he is competing for conservative votes along with former Arkansas Govenor Mike Huckabee. Mr Huckabee said Mr Romney should recognize him as the true conservative and get out of the race.