Washington (CNN) -- Front-runners Mitt Romney and Newt Gingrich traded accusations of dishonesty Sunday as the increasingly vitriolic Republican presidential campaign headed for its biggest primary to date.
With two days to go before Florida voters decide who gets the state's winner-take-all 50 delegates, Romney held a widening lead over Gingrich in the competition to become the first of the four remaining candidates to win two contests in this year's nominating process.
With former Pennsylvania Sen. Rick Santorum canceling campaign events Sunday because of his young daughter's hospitalization and Texas Rep. Ron Paul forgoing Florida to focus on Maine, Romney and Gingrich shared the spotlight in the Sunshine State and continued to ratchet up the rhetoric.
Stung by Romney's resurgence, which has benefited from strong debate performances last week and advertisements that harshly attacked Gingrich, the former House speaker accused Romney of waging a dishonest campaign.
"He would say thing after thing after thing that just plain wasn't true," Gingrich said of the former Massachusetts governor in reference to last Thursday debate's on CNN. "I don't know how you debate a person with civility if they're prepared to say things that are just plain factually false. "
In particular, Gingrich cited Romney's claim that he had never voted for a Democrat when a Republican was on the ballot, including Romney's support for Democrat Paul Tsongas in the 1992 Massachusetts presidential primary.
Incumbent President George H.W. Bush and conservative commentator Pat Buchanan were on the GOP ballot in the primary, but Romney has said he registered as an independent and voted for Tsongas as a strategic move against Bill Clinton.
"He can't even remember his own voting record," Gingrich said Sunday on the ABC program "This Week."
"The debate the other night, what he said was just plain false."
To Gingrich, such a statement by Romney raised questions about Romney's suitability to be president.
"You cannot be president of the United States if you cannot be honest and candid with the American people," Gingrich said. "And that's compounded, frankly, by a number of the ads he runs, which are just plain false."
In particular, Gingrich cited claims in Romney ads that he resigned in disgrace from the House in 1999 after being cited two years earlier for an ethics violation.
"I did not resign in disgrace," Gingrich declared, and he also rejected the assertion that the $300,000 he paid to cover the cost of the investigation against him was a fine.
Romney's campaign responded that Gingrich, a historian, was trying to "rewrite history."
"He admitted to violating House rules and providing false and misleading information to the ethics committee," said an e-mail from Romney spokeswoman Andrea Saul. "He released a statement saying he was wrong and agreed to pay a $300,000 penalty. He said, 'My actions did not reflect creditably on the House of Representatives.' Nearly 90% of House Republicans agreed."
At a Naples, Florida, campaign event Sunday, Romney touted his debate performances in Florida, drawing cheers by asking: "Wasn't that a hoot?"
Referring to Gingrich's complaints about the two Florida debates, including the former House speaker's protest against organizers telling the audience to keep quiet at the first one last Monday, Romney said Gingrich was "now finding excuses everywhere he can" for his falling support.
"My own view is the reason that Speaker Gingrich has been having a hard time in Florida is that people of Florida have watched the debates, have listened to the speaker, have listened to the other candidates and have said, 'You know what, Mitt Romney's the guy we're going to support,'" he said.
Romney also revived an attack on Gingrich's past consulting work for troubled mortgage giant Freddie Mac, and in doing so, highlighted the housing crisis that has ravaged Florida.
"Your problem in Florida is that you worked for Freddie Mac at a time when Freddie Mac was not doing the right thing for the American people," Romney said. "And that you're selling influence in Washington at a time when we need people who will stand up for the truth in Washington."
The sharp campaign attacks caused some Republicans to lament infighting that they fear will hurt the surviving candidate's chances of defeating President Barack Obama in November.
Veteran Sen. John McCain of Arizona, the Republican presidential nominee in 2008, called for a halt to the GOP debates -- 19 so far this campaign dating back to May -- that he said emphasized infighting.
"Unfortunately, they have deteriorated into wrestling matches and that's not what the voters want to hear to start with, but second of all, it has driven the negatives, the 'unfavorables' of all of our candidates in these debates way up, and uh, look, that detracts from you ability to take on the real opponent, which is Barack Obama," McCain said.
On the CBS program "Face the Nation," real estate tycoon Donald Trump also noted what he called "a very nasty race."
"The level of hatred, I guess you could say, there's no other word for it, it's unbelievable," Trump said, adding that the eventual GOP winner might emerge a stronger candidate, but it was "very possible they're hurting themselves."
In addition, Trump -- who has in the past expressed interest in running for president but never followed through -- again raised the possibility of mounting an independent campaign if he believes the Republican nominee would be unable to beat Obama.
Gingrich argued Sunday that even though Romney is leading, the conservative supported reflected by backing for himself and Santorum exceeded Romney's support, according to the latest polls.
One poll that came out Sunday morning and straddled the Thursday night CNN debate in Jacksonville, showed Romney at 42%, Gingrich at 27%, Santorum at 16% and Paul at 11%.
Romney also led in a Tampa Bay Times/Miami Herald/Bay News 9 survey of likely GOP voters conducted January 24 through January 26 -- before the CNN debate -- and released Saturday evening. Romney received 42% to 31% for Gingrich, 14% for Santorum and 6% for Paul.
"We have no evidence yet that Romney anywhere is coming close to getting a majority and I think when you take all the non-Romney votes, it's very likely that at the convention there will be a non-Romney majority and maybe a very substantial one," Gingrich told reporters. "My job is to convert that into a Gingrich majority."
On Saturday, Gingrich received the endorsement of tea party favorite Herman Cain, who cited the former speaker's "big ideas" and his willingness to go through what he called the "sausage grinder" of the campaign process.
'I know what this sausage grinder is all about," said Cain, a businessman who dropped out of the race after allegations of sexual harassment in his past. "I know that he is going through this sausage grinder because he cares about the future of the United States of America."
Meanwhile, Santorum canceled a series of events -- including an interview on NBC's "Meet the Press" -- after his 3-year-old daughter Isabella was admitted to a Philadelphia hospital.
The girl, known as Bella, suffers from a chromosomal condition called Trisomy 18 caused by extra material from chromosome 18. It is three times more common in girls than boys, and patients who survive past the first week experience serious medical and developmental problems, according to the National Institutes of Health.
Running a distant third in Florida polling, Santorum insists he will continue in the race. So far in the campaign, Santorum narrowly defeated Romney to win the Iowa caucuses, while Romney won the New Hampshire primary and Gingrich won the South Carolina primary.
Paul, who has conceded Florida because he knew he had no chance in the state's winner-take-all format, campaigned Saturday in Maine for caucuses taking place there through February 11.
He told CNN's "State of the Union" on Sunday that he expects to do well in Maine, but acknowledged he lacks the financial backing to compete head-on in every state.
"The rough road isn't, you know, presenting our case," Paul said. "The rough road is competing with, you know, establishment money, the big money. ... We can raise those millions, but we can't compete with tens of millions of dollars for each individual state. And that's what, you know, came up in Florida. You need a lot of money. So it's a money game. And I think that's one of the things that frustrates a lot of people."
CNN's Gabriella Schwarz, Gregory Wallace, Rachel Streitfeld and Shawna Shepherd contributed to this report.