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Mitt Romney started the day in Florida Tuesday with a detailed explanation of his tax returns but benefiting from a strong performance in a debate the night before in which he went on the offensive against Newt Gingrich, calling the former speaker a failed leader who resigned in "disgrace."

After getting trounced in South Carolina's Republican presidential primary election -- and expressly hoping to avoid a similar outcome in Florida -- Romney said he can't just sit back and take attacks from his rivals -- and he didn't.

Instead, he went after Gingrich, argued that the former speaker was forced out of Congress because of ethics problems and an inability to corral his caucus. He also suggested that after leaving Congress, Gingrich was an "influence peddler" for taking consulting jobs whose purpose was to advise groups like Freddie Mac about how to approach lawmakers.

"His contract with Freddie Mac was provided by the lobbyists at Freddie Mac. I don't think we can possibly retake the White House if the person who's leading our party is the person who was working for the chief lobbyist of Freddie Mac," Romney said at the debate held in Tampa, Fla., home to the Republican National Convention this summer and a key voting center in the Sunshine State's Jan. 31 primary.

"Freddie Mac was paying Speaker Gingrich $1,600,000 at the same time Freddie Mac was costing the people of Florida millions upon millions of dollars," he continued.

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Gingrich, who released his contract with the mortgage giant ahead of the debate in an effort to blunt criticism, retorted that Romney as a businessman surely knows the difference between his company earning money and him personally collecting on the contract. He also defended the work as being consulting, not lobbying.

"The governor did consulting work for years. I have never suggested his consulting work was lobbying," he said. "There is no place in the contract that provides for lobbying. I have never done any lobbying."

A more subdued Gingrich, who didn't have audience participation to egg him on since NBC host Brian Williams told the crowd not to make any noise or applause, tried to return volley suggesting that the work Romney did for private equity firm Bain Capital as a consultant was no different from his own. He also defended government-sponsored enterprises that he said have done good things for America.

Romney suggested that Gingrich couldn't lead the charge against President Obama on behalf of the GOP because his own House caucus had rejected him as its leader.

"I think it's about leadership, and 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

Gingrich responded that Romney was wrong on the facts.

"I left the speakership after the 1998 election because I took responsibility for the fact that our results weren't as good as they should be. I think that's what a leader should do," Gingrich said.

"The fact is, on every single ethics charge of substance that was dismissed in the end, the only thing we did wrong is we had one lawyer (write a letter) ... and the one letter was in error. I didn't pay a fine. I paid the cost of going through the process of determining it was wrong," he said.

The former Massachusetts governor has said the 2010 tax returns and estimate for 2011 that he was releasing on Tuesday would show that he paid about a 15 percent effective rate. In actuality, the returns, released overnight, showed an effective rate of 13.9 percent in 2010 and an estimated 15.4 percent in 2011, or $6.2 million in taxes being paid on $42.6 million in income for 2010 and 2011. Most of that income came from investments held in a blind trust. He also contributed about $7 million in donations to his church and other charities.

Romney said Monday night he wouldn't pay a penny more in taxes than required by law, and didn't think America would want a president who gives the government more money than it is owed.

Romney added that he's proud of his success because he made it on his own, and built his wealth by helping people get jobs.

"I earned it the old fashioned way, by working hard," he said.

While Romney and Gingrich fought one another, they also had to cede time to Rick Santorum and Ron Paul, the other candidates in the final four who've strongly influenced the race but who have not received as much face time lately as the front-runners.

Asked to explain how he could win the presidency when he couldn't win re-election in his own Senate race in Pennsylvania, Santorum, the winner of the Iowa caucuses, said it was a "meltdown" year for Republicans, who had historic losses in the statehouse, lost five congressional seats in the Pennsylvania delegation and lost 23 out of 33 U.S. Senate seats nationwide.

"Probably unlike a lot of other candidates, when you're running in an election year that you know you're running against a headwind, a lot of folks crouch down, they get out of the way of the wind and try to sneak in. I stood tall, stood for what I believed in," he said. "There's one thing worse than losing an election, and that's not standing for the principles that you hold."

Paul who called the Iowa results not much more than a "straw vote" said he has more support from people under 30 than any of the other candidates and can give President Obama a run for his money on it. Paul said he is not thinking of becoming a third party candidate because he is not an "absolutist."

Paul added that while he and Gingrich agree on some items, they disagree on fundamentals of foreign policy.

"He keeps hinting about attacking the Fed, and he talks about gold. Now if I could just change him on foreign policy, we might be able to talk business," Paul said.

Paul also separated himself from his rivals on Cuba, a big issue for Florida voters, including many Cuban-Americans in the state who are Republicans. The Texas congressman, who served in the military in 1962 at the height of the Cuban Missile Crisis, said the United States propped up Cuba's Castro regime because "we put on these sanctions and this -- only used as a scapegoat."

But Romney said that relaxing relations with Cuba is "dangerous" at this point.And Gingrich said U.S. policy should be to "aggressively" pursue overthrowing the regime. Santorum said sanctions should remain "until the Castros are dead."