(CNN) -- The remaining contenders for the presidency kicked off their final maneuvers for Super Tuesday, fine-tuning their closing messages in appearances on the Sunday talk shows and fanning out across the nation for an exhaustive list of last-minute campaign stops.
Sens. Barack Obama and Hillary Clinton are fighting for the Democratic nomination.
Sen. John McCain of Arizona expressed some hope of clinching his party's nomination Tuesday -- and, minutes later, found himself speaking on live national television with Sen. Hillary Clinton of New York, who has vowed she is the Democrat best prepared to beat him in a general election.
Smiling and exchanging pleasantries briefly on "Fox News Sunday," the two -- apparently unaware they'd appear together live between their separate interviews from different cities -- vowed that if selected for their parties' nominations they would have a "respectful" debate focusing on serious "differences."
Clinton is locked in a neck-and-neck race with Illinois Sen. Barack Obama. McCain has a clear lead in the polls heading toward Tuesday, but is facing stepped-up attacks by former Massachusetts Gov. Mitt Romney.
Asked whether he will win the nomination Tuesday, McCain said, "I hope so. But you know, you don't know for sure. I think we got a lot of good momentum and a lot of endorsements and crowds who are enthusiastic, and we're working hard, and I'm guardedly optimistic."
Clinton, meanwhile, focused on her platform, talking to Fox and ABC about her plans for universal health care and the economy. Watch Clinton, Obama spar »
Working to draw a distinction from Obama, she told ABC's "This Week," "I've been taking the incoming fire from Republicans for about 16 years now, and I'm still here because I have been vetted; I have been tested."
Obama, on CBS' "Face the Nation," reiterated his argument that because many Republicans consider Clinton "polarizing," he stands a better chance of drawing "independents and others that Clinton cannot."
Obama's campaign, fueled by momentum from his South Carolina primary victory and a heavy influx of donations in January, faced a new twist Sunday when The New York Times ran a front-page story examining Obama's work in the Senate involving radioactive leaks in Illinois. On his Web site, the campaign challenged the story.
But a series of polls showing him closing the gap on Clinton's national lead -- including in California, the most delegate-rich prize in Tuesday's race -- left Obama's campaign enthusiastic about his prospects to clinch a large number of delegates Tuesday.
While Obama was in Delaware and Clinton had stops in Missouri and Minnesota, both had their superstar surrogates at work in California. Former President Bill Clinton visited several predominantly African-American churches in Southern California, while Oprah Winfrey planned to take part in a rally for Obama in Los Angeles.
The former president also plans to watch the Super Bowl with former Democratic presidential contender Bill Richardson, a popular figure in the Latino community. Richardson has not endorsed a candidate since dropping out of the race. Latinos are a core constituency for Clinton, though Obama has fought to win over Latinos, partly with the help of Sen. Ted Kennedy.
If Clinton and Obama split delegates in Tuesday's Democratic contests in 22 states and American Samoa, the Democratic contest could easily last weeks more. See how Super Tuesday is broken down »
Romney, hoping to force a similar situation on the GOP side -- where 21 states will hold their contests -- fought to capitalize Sunday on the frustration many conservatives feel with McCain.
He told CNN's "Late Edition with Wolf Blitzer" that "conservative voices, both from radio and from publications, are saying, 'You know what, we've got to get behind Mitt Romney. We really can't afford John McCain as the nominee of our party.'" Watch a closer look at the candidates as they approach Super Tuesday »
"And that kind of groundswell, I think, is what led me to win in Maine yesterday."
The Maine caucuses are still under way, and CNN has not projected a winner. Early results showed Romney with a lead.
Former Arkansas Gov. Mike Huckabee, a conservative who trails in national polls, rejected any suggestions that he may soon drop out.
"I think people need to remember that the people are going to make this choice, not the national pundits," he told CNN's "Late Edition."
Huckabee added, "Come Tuesday, we feel like we are going to pick up quite a few delegates and do very well. And we are going to keep going."
Huckabee was in Georgia Sunday, while McCain was in Connecticut and Romney had events in Illinois and Missouri.
No major public events were scheduled at nighttime however. It seemed no candidate wanted to compete with the Super Bowl. E-mail to a friend