Although the upcoming presidential debates won't change how most people vote, 18 percent of voters recently surveyed say they may very well change their vote based on how well the two candidates do.

In a new FOX News/Opinion Dynamics poll, 77 percent of 1,000 likely voters surveyed said their minds were made up in the fight between President Bush (search) and Sen. John Kerry (search). Recent polls show that Bush has a slight edge on Kerry in overall support.

The candidates meet for the first time Thursday night, when the focus is on foreign policy and homeland security. The debate will be aired live on FOX News Channel at 9 p.m. EDT.

That will be followed by a general debate on Oct. 8 and a final debate Oct. 13 that focuses on the economy.

Bush and Kerry spent Tuesday out of the public eye as they prepared for their first debate, with Bush doing his homework at his ranch in Crawford, Texas, and Kerry studying in Wisconsin.

Asked whom they expect to do better in the face-off, 39 percent said Kerry and 37 percent said Bush. Ten percent said both candidates would do the same while 14 percent were not sure.

But a clearer split emerges when asked who will do better in the Oct. 5 vice presidential debate between Vice President Cheney (search) and Sen. John Edwards (search). Edwards, a Democrat from North Carolina, gets the advantage from 45 percent of respondents, while 35 percent think Cheney will do better.

Point, Counter Point

While the candidates kept out of sight Tuesday, their surrogates made the media rounds.

"John Kerry is going to attack the issues in the debate. That's something this country has been waiting for for four long years," Kerry strategist Tad Devine told FOX News.

Devine said Bush had not been clear with the public about such issues as Iraq and intelligence, but Bush strategist Matthew Dowd said Kerry has the toughest challenge.

"In the end, they trust the president on Iraq, on terror and the economy," Dowd said. "What John Kerry has to do in 90 minutes is what he hasn't been able to do in two years, which is come across as credible."

But Devine argued that Kerry has been clear about his views on Iraq and has laid out a plan to get the United States out of what Devine described as a "quagmire."

"The real stunner at the debate is whether the president will admit to making a single mistake," Devine said.

Dowd responded that voters were not interested in such a declaration.

"The public doesn't want someone who is going to lay down on a psychiatrist's couch and rethink everything that's happened," Dowd said. "John Kerry has vacillated so much and explored every single nuance of every single policy decision that no one knows what he stands for."

Candidates Test Themes

On Monday, the two candidates auditioned themes certain to come up at the 90-minute showdown in Coral Gables, Fla.

Speaking at a town-hall style meeting, not far from the hideaway resort where he is preparing for the debate, Kerry ridiculed Bush for telling FOX News' Bill O'Reilly that he had no regrets over his "mission accomplished" speech aboard an aircraft carrier — and would do it again.

"Since he said that, over 900 have given their lives for the country. The mission was not accomplished when he said it," Kerry said.

"He didn't know it and didn't understand it. It's not accomplished today. And he's still trying to hide from the American people what needs to be done in order to be successful in Iraq," Kerry added. Bush didn't actually say "mission accomplished" at the time, but spoke beneath a huge banner on the carrier bearing those words.

Bush was asked whether he would still give that May 1, 2003, speech, knowing what he knows now. "Absolutely," he replied.

Click to read a transcript of the interview: Part 1 | Part 2

In another part of the interview, Bush told FOX News that the situation in Iraq is "tougher than heck right now" because terrorists are killing innocent Iraqis and U.S. soldiers "in order to try to get us to leave." If the United States wavers, the situation will get worse, he said. "That's what the terrorists are watching, they're watching us like hawks."

Part two of the three-part interview airs Tuesday at 8 p.m. EDT on the FOX News Channel.

Bush sounded a favorite theme at a rally at the Midwest Lifestock and Expo Center in Springfield, Ohio: Kerry has vacillated repeatedly on Iraq. "You cannot expect to lead this world if you try to take both sides of every position," Bush said.

Referring to the face-off scheduled for Thursday night, Bush said, "He probably could spend 90 minutes debating himself. It's been a little difficult to prepare because he keeps changing positions on the War on Terror."

Both Bush and Kerry used caustic humor to prod each other. Kerry told his Wisconsin audience not to be wary of changing horses midstream — if the horse is drowning. "May I also suggest that we need a taller horse? You can get through deeper waters that way," he said, a reference to his five-inch height advantage over Bush.

FOX News' J. Jennings Moss and The Associated Press contributed to this report.