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Charles Dharapak, Associated Press
Republican presidential candidate, former Massachusetts Gov. Mitt Romney speaks to reporters after holding a discussion on housing and foreclosure, Monday, Jan. 23, 2012, in Tampa, Fla.

TAMPA, Fla. — Rocked in South Carolina over the weekend, an increasingly aggressive Mitt Romney looked to take the fight to Newt Gingrich in debate Monday night as the combative Republican presidential contest shifted farther south to Florida.

The fireworks began before they walked onto the debate stage.

Romney began running an ad that said Gingrich "cashed in" with home-loan giant Freddie Mac while Floridians were being crushed in the housing crisis.

Gingrich mocked Romney as someone campaigning on openness "who has released none of his business records."

Gingrich, the former House speaker, has suddenly seized the nomination momentum, following weak finishes in Iowa and New Hampshire with the solid victory over Romney Saturday in South Carolina. And recent Florida polls suggest he may have erased Romney's lead here.

While the fight has largely become a two-man contest, they will share the stage with former Pennsylvania Sen. Rick Santorum and Texas Rep. Ron Paul.

The GOP rivals were clashing at the University of Southern Florida Monday night and will meet again Thursday night in the run-up to the Florida primary on Tuesday, Jan. 31. The winner of the nomination will face Democratic President Barack Obama in November.

Before the Tampa debate started, Romney went after Gingrich in person and on the Florida airwaves.

At a campaign stop, Romney likened Gingrich to a pinball machine and suggested the former House speaker engaged in "potentially wrongful activity" in his consulting work over the past decade.

Romney then released his first negative ad of the campaign.

"While Florida families lost everything in the housing crisis, Newt Gingrich cashed in," the TV ad says, noting that the former speaker made more than $1.6 million working for Freddie Mac. "Gingrich resigned from Congress in disgrace and then cashed in as a D.C. insider."

Gingrich never registered as a lobbyist, but said he was a consultant for Freddie Mac, the federally backed mortgage company that played a significant role in the housing crisis.

It remains to be seen if Romney can effectively use his newly aggressive stance on the debate stage, a forum in which Gingrich has excelled so far. Underfunded and overmatched by Romney's massive ground game across the country, Gingrich has relied upon strong debate performances to build support.

It appears Romney has brought in outside help to improve his debate technique.

Veteran debate coach Brett O'Donnell was spotted at a Romney campaign stop on Monday. He previously advised President George W. Bush and GOP nominee John McCain and was a senior adviser and speech writer for Michele Bachmann's abbreviated campaign.

Gingrich, meanwhile, is showing no signs of backing down.

During an appearance on ABC's "Good Morning America," he referred to Romney as "somebody who has released none of his business records, who has decided to make a stand on transparency without being transparent." After initially balking, Romney is set to release personal tax records on Tuesday.