Updated 10:56 p.m. ET

The long-awaited showdown between Newt Gingrich and Mitt Romney erupted into a slugfest at a Republican presidential debate in Florida, setting a combative tone in the campaign ahead of the state's Jan. 31 primary. 

The former House speaker and the former Massachusetts governor began sniping early at Monday evening's NBC News/National Journal/Tampa Bay Times debate; they carried on through much of the debate before finding more conciliatory turf when answering questions specific to the state of Florida. 

Still, the gathering delivered what had been expected: Romney taking a new, aggressive tack against Gingrich, and Gingrich finding himself in the frontrunner's spotlight after having scored a decisive victory in last weekend's South Carolina primary. 

The sharpest exchange over the evening came over Gingrich's work on behalf of troubled mortgage giant Freddie Mac. Romney had assailed that work, which earned Gingrich's consulting firm a lucrative contract, on the campaign trail, and repeated it tonight. 

• Romney earned $42.5M, will pay $6.2M tax bill

"The fact is I offered strategic advice, largely based on my knowledge of history, including the history of Washington," Gingrich said of his work. (His campaign released a copy of his contract with Freddie Mac this evening at the behest of the Romney campaign.)

Romney insisted that Gingrich's advocacy work on behalf of Freddie Mac — as well as the ex-speaker's push for a prescription drug benefit in Medicare during a legislative battle in 2003 — represented nothing more than lobbying by another name.

"If you're getting paid by health companies … and you then meet with Republican congressmen and encourage them to support that legislation, you can call it whatever you'd like. I call it influence-peddling," Romney said. "It is not right. It is not right. You have a conflict."

The sparring between Romney and Gingrich was reflective of the uncertainty injected into the primary campaign by Gingrich's victory in South Carolina. None of the four candidates onstage tonight in Tampa has won more than a single nominating contest, and the campaign now threatens to extend into Super Tuesday and beyond.

Romney had sent every signal between Saturday night and Monday evening's debate that he planned to take a more aggressive tack against Gingrich as part of an effort to halt the former speaker's momentum in Florida, which isn't just a key primary state, but a pivotal swing state in the general election, as well. 

'Historic losses'
Romney launched into the criticism in his very first answer, assailing Gingrich as an unreliable conservative who could embarrass the GOP.

"The speaker was given an opportunity to be the leader of our party in 1994. And at the end of four years, he had to resign in disgrace," Romney said. 

"Don't forget at the end of the speaker's term as speaker, his approval rating was down to 18 percent. We suffered historic losses after his four years in office," Romney added.

For his part, Gingrich opened on a more optimistic note and appeared reluctant at first to engage Romney's attacks.

"I'm not going to spend the evening trying to chase Gov. Romney's misinformation," Gingrich said, explaining his campaign would provide rejoinders on its website tomorrow morning. "He just said four things that were false. I don't want to waste any time on them."

But any hopes for a high-brow affair quickly disappeared when Gingrich sharply disputed Romney's account of his speakership: "He may have made a good financier. He's a terrible historian."

It was the kind of red-hot fight most political observers had expected after the GOP presidential primary was thrown into upheaval by the former House speaker's victory in this past weekend's in South Carolina.

The debate was one of the fiercest battles of the Republican campaign, presaged by a day of sniping on the campaign trail that saw the Romney and Gingrich trade rhetorical blows in a preview of the new phase of the GOP campaign. 

The Romney campaign is hoping Florida proves to be a firewall against Gingrich's surge. They've spent millions on advertising in the state, and Romney has enjoyed an early advantage in the polls — one his campaign hopes transfers to the over 225,000 early and absentee ballots that have been cast. 

But the voting is limited to registered Republicans only, meaning the electorate might be composed of the more conservative voters that fueled Gingrich's win in South Carolina. Gingrich is hoping that twin victories in South Carolina and Florida would decimate the aura of inevitability Romney built around his campaign. 

Texas Rep. Ron Paul has elected against participating in Florida with much vigor. He spent most of the debate voicing his usual message, decrying government spending and U.S. involvement in foreign conflicts.

Former Pennsylvania Sen. Rick Santorum, the winner of the Iowa caucus by the slimmest of margins, put himself forward at the debate as the only true conservative. He went on the attack against Gingrich and Romney by saying there is little different between them and President Obama.

"They rejected conservatism when it was hard to stand. It's going to be hard to stand whoever this president is going to be elected," Santorum said, echoing that same line of attack at the end of the debate. "There is no difference between President Obama and these two gentlemen. And that's why this election in Florida is so critical, that we have someone that actually can create a contrast between the president and the conservative point of view."

Romney, on the attack for much of the night, stumbled on a question regarding how he would handle illegal immigrants residing in the United States. 

"Well, the answer is self-deportation, which is people decide they can do better by going home because they can't find work here because they don't have legal documentation to allow them to work here," Romney said, raising eyebrows if nothing else than for the opacity of the concept. "And so we're not going to round people up."