"Mitt Romney has proven in this campaign that he will say anything to anyone at anytime if he thinks it will help him politically. His stunning capacity to reverse his position on virtually every issue casts serious doubt on his ability to lead. Floridians need to ask themselves: If he changes his position today, what prevents him from reversing himself again tomorrow?" according to a statement from McCain communications director Jill Hazelbaker. "Today, desperate to attack John McCain in the heat of a political campaign, Mitt Romney has changed his position once again."

McCain's campaign latched onto the "flip-flopper" tag often given to Romney, saying that two years ago he fully supported a "cap and trade" system to deal with global climate change. McCain's campaign quoted him as saying, "I'm convinced it is good business," and said Romney cited its "positive effect on development of technologies and economic growth."

McCain also released a Web ad on YouTube called a "Tale Of Two Mitts" showing video clips from Romney's 1994 Senate race against Sen. Ted Kennedy, D-Mass., and other video that appear to contradict statements made in 2007 while campaigning for the White House.

After a rally in Sanford, Fla., Monday afternoon, Al Cardenas, chairman of the Romney campaign in Florida, said the campaign received word from supporters that they were getting automated calls saying that Romney was in favor of opening relations with Fidel Castro in Cuba. The source of the calls was unknown.

Cardenas said it was a "dirty tactic and strategy" and while he did not outright say the McCain campaign was behind it, he said that only the Romney and McCain campaigns were doing automated calls in the state.

McCain spokeswoman Crystal Benton said the calls were not being made by the campaign. She said, though, that automated calls that say they were from the Romney campaign were inaccurately characterizing McCain's record on abortion. Benton said, noting McCain has a 24-year pro-life record."

The back and forth between McCain and Romney lasted all day.

In a send-off rally at the West Palm Beach airport, Romney was back painting McCain as a liberal, pointing to the fact he one time considered being Sen. John Kerry's running mate on the Democratic ticket in 2004.

"Had someone asked me that question, there would not have been a nanosecond of thought about it; it would have been an immediate laugh," Romney said. "And, of course, if someone asked him if he would consider me as a running mate, he would have also laughed immediately."

During an airport stop at Fort Myers, Romney told a crowd of supporters that McCain has pressed for legislation that "would have pulled the nation to the left. I just don't think those liberal answers are what America is looking for," Romney said.