Mitt Romney on the attack

Republican presidential candidates former Massachusetts Gov. Mitt Romney, left, gestures as he talks to former House Speaker Newt Gingrich during a Republican presidential debate Monday Jan. 23, 2012, at the University of South Florida in Tampa, Fla.

TAMPA, Fla. -- Mitt Romney had a lot to lose going into Florida's first Republican presidential debate Monday night, after seeing his lead in South Carolina evaporate after two dominant debate performances by Newt Gingrich, who won the primary there.

Gingrich's entire campaign so far has been fueled by the debates. He finished fourth in Iowa, but there were no debates for two weeks before the voting. Then came South Carolina.

Monday night offered another opportunity for Gingrich to tee up Florida, but he was flat -- and that was good news for Romney, who was crisp, authoritative -- and on the offensive, in what was probably his best debate performance so far.

Romney immediately went after Gingrich, saying he couldn't win the general election in November, in part due to Gingrich's ties to Freddie Mac.

Romney argued that Gingrich was just another Washington insider, lobbying on behalf of a mortgage giant that helped trigger the housing crisis.

Special section: Election 2012

Gingrich took issue with that, saying he'd never "done any lobbying," and saying records from his Freddie Mac contract -- released just before the debate -- back him up.

Romney was pressed anew on his tax returns - which were being released Tuesday morning, showing he made more than $40 million over the past two years -- almost all of it from investments. He paid $6.2 million in federal taxes during that time, and gave $7 million to charity -- including at least $4 million to the Latter Day Saints church. His tax rate: 13.9 percent in 2010.

Romney said he pays "all the taxes that are legally required and not a dollar more."

Though Rick Santorum and Ron Paul took some swipes at the others, the main event, as expected, was between Romney and Gingrich.

To see Jan Crawford's report, click on the video above.

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    Jan Crawford is CBS News Chief Legal Correspondent.