Former Pennsylvania Sen. Rick Santorum, trailing in Florida by a wide margin, stayed with his 3-year-old daughter, Bella, who was hospitalized with pneumonia. Sunday night he told supporters, "She without a doubt has turned the corner," but he cautioned she "isn't out of the woods yet."

Gingrich's consulting firm was paid more than $1.5 million by the federally-backed mortgage company over a period after he left Congress in 1999.

"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, and that you're selling influence in Washington at a time when we need people who will stand up for the truth in Washington," Romney told an audience in Naples.

Romney continued to paint Gingrich as part of the very Washington establishment he condemns and someone who had a role in the nation's economic problems.

Gingrich objected specifically to a Romney campaign ad that includes a 1997 NBC News report on the House's decision to discipline Gingrich, then speaker, for ethics charges.

"I don't know how you debate a person with civility if they're prepared to say things that are just plain factually false," Gingrich said during appearances on Sunday talk shows. "I think the Republican establishment believes it's OK to say and do virtually anything to stop a genuine insurgency from winning because they are very afraid of losing control of the old order."

Gingrich reacted defensively, accusing the former Massachusetts governor and a political committee that supports him of lying, and the GOP's establishment of allowing it.

Romney's campaign has dogged Gingrich at his own campaign stops, sending surrogates to remind reporters of Gingrich's House ethics probe in the 1990s and other episodes in his career aimed at sowing doubt about his judgment.

An NBC News/Marist poll published Sunday showed Romney with support from 42 percent of likely Florida primary voters, compared with 27 percent for Gingrich.

In what has become a wildly unpredictable race, the momentum has swung back to Romney, staggered last weekend by Gingrich's victory in South Carolina. Romney has begun advertising in Nevada ahead of that state's caucuses next Saturday, illustrating the challenges ahead for Gingrich, who has pledged to push ahead no matter what happens in Florida.

And despite surging ahead in polls, Romney wasn't letting up, relentlessly casting Gingrich as an influence peddler with a "record of failed leadership."

POMPANO BEACH, Fla.—Newt Gingrich slammed GOP rival Mitt Romney on Sunday for the steady stream of attacks he likened to "carpet-bombing," trying to cut into the resurgent front-runner's lead in Florida in the dwindling hours before Tuesday's pivotal presidential primary.

Texas Rep. Ron Paul, who has invested little in Florida, looked ahead to Nevada. The libertarian-leaning Paul is focusing more on gathering delegates in caucus states, where it's less expensive to campaign. But securing the nomination only through caucus states is a hard task.

The intense effort by Romney to slow Gingrich is comparable to his strategy against Gingrich in the closing month before Iowa's leadoff caucuses Jan. 3. Gingrich led in Iowa polls, lifted by what were hailed as strong performances in televised debates, only to drop in the face of withering attacks by Romney, aided immensely by ads sponsored by a "super" political action committee run by former Romney aides.

But Romney aides say they made the mistake of assuming Gingrich could not rise again as he did in South Carolina. Romney appears determined not to let that happen again.

"His record is one of failed leadership," Romney told more than 700 people at a rally in Pompano Beach Sunday evening. "We don't need someone who can speak well perhaps, or can say things we agree with, but does not have the experience of being an effective leader."

Gingrich has responded by criticizing Romney's conservative credentials. Outside an evangelical Christian church in Lutz, Gingrich said he was the more loyal conservative on key social issues.

"This party is not going to nominate somebody who is a pro-abortion, pro-gun-control, pro-tax-increase liberal," Gingrich said. "It isn't going to happen."

But Gingrich, in appearances on Sunday news programs, returned to complaining about Romney's tactics. "It's only when he can mass money to focus on carpet-bombing with negative ads that he gains any traction at all," he said.

Romney and the political committee that supports him had combined to spend some $6.8 million in ads criticizing Gingrich in the Florida campaign's final week. Gingrich and a super PAC that supports him were spending about one-third that amount.

Gingrich worked to portray himself as the insurgent outsider, collecting the endorsement of tea party favorite Herman Cain, whose own campaign for president foundered amid sexual harassment allegations.

It was unclear how aggressively Gingrich would be able to compete in states beyond Florida. The next televised debate, a format Gingrich has used to his advantage, is not until Feb. 22, more than three weeks away.

Romney already has campaigned in Nevada more than Gingrich, is advertising there, and stresses his business background in a state hard-hit by the economy. His campaign welcomed the Sunday endorsement of the Las Vegas Review-Journal, Nevada's largest newspaper.

Michigan and Maine, where Romney won during his 2008 campaign, also hold their contests in February. Arizona, a strong tea-party state where Gingrich could do well, has its primary Feb. 28.

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Associated Press writers Steve Peoples in Naples and Shannon McCaffrey in Lutz contributed to this report.

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