At a polling station in St. Petersburg, Fla., this morning, McCain took some last digs at Romney when asked about the rising level of vitriol between the rivals.
"It's only been Gov. Romney who decides to attack opponents when he thinks they are moving up and succeeding," McCain said, reports ABC News' Bret Hovell. "That's just the way he campaigns; it's just a matter of record."
Asked how he was feeling, McCain touted his endorsement from Florida's Republican governor, Charlie Crist.
"I'm feeling good. Endorsements matter," McCain said. "It would have been very easy for Gov. Crist to say, 'I'm not going to get into a contested primary.' I'm very grateful and very appreciative."
Romney kept up his attack on McCain Tuesday but didn't mention him by name.
"One of the candidates out there running for president said that the economy is not his strong suit. Well, it's my strong suit," Romney told supporters at a campaign rally in Tampa, Fla., reports ABC News' Matt Stuart.
"I think it's helpful to have a president of the United States who actually has been in the real economy if he's gonna try and fix the real economy," Romney said, continuing his strategy of touting his business credentials.
Preliminary exit poll results suggest the economy emerged as a top concern for Republican primary voters in Florida, as it has throughout this primary season. About 40 percent of voters said they were looking chiefly for a candidate who "shares my values" and just over 30 percent said they wanted a candidate who "has the right experience."
Former Gov. Mike Huckabee, who has yet to repeat his win in Iowa, has said he is trying to stay in the race until Feb. 5, where he may be in a better position to wage a delegate war with his rivals.
"It's an important vote just to keep us in the game. We know that right now going into today that we may not be leading in the polls, but we expect to come out of here still on our feet, and that's what's important to us," Huckabee said today in Tampa, reports ABC News' Kevin Chupka. "Next week, when we have a lot of Southern states in play and we're leading in all those states, it's going to be a really big day for us to pick up delegates."
Going into the Feb. 5 races with a strong campaign was seen as important because of the cost of competing in more than 20 states.
"No one, not even Mitt Romney, can afford saturation advertising across California and 20 other states all at the same time," Schnur said. "So while Romney will have a significant paid-media advantage, a win for McCain in Florida would largely erase that in terms of the news coverage and public attention he'd be getting."
ABC News' John Berman, Peyton Craighill, Jake Tapper, Rick Klein, Jan Simmonds, Bret Hovell, Kevin Chupka, Eloise Harper and Matt Stuart contributed to this report.