TAMPA – Mitt Romney has taken his gloves off.

Romney on Tuesday lodged his first attack on his surging rival, Newt Gingrich, by labeling the former House speaker “a lifelong politician” and suggesting he lacks credibility on the economy.

View Photo Gallery: November on the campaign trail with #2012Unfiltered. Above, stagecraft for Mitt Romney’s campaign stop in Miami. A trio of Cuban-American Republicans endorsed Romney at the event, held at a papaya wholesaler’s warehouse.

Asked by Fox News’s Bret Baier in an interview Tuesday whether Gingrich could beat President Obama, Romney said: “I think to get President Obama out of office, you’re going to have to bring something to the race that’s different than what he brings.”

“He’s a lifelong politician. I think you have to have the credibility of understanding how the economy works. And I do. And that’s one reason I’m in this race.”

Among the Republicans running for president, Romney said that he believes he has the best shot “by far” of defeating Obama. He called Gingrich “a good man,” but highlighted the differences in their backgrounds.

“He spent his last 30 or 40 years in Washington,” Romney said. “I spent my career in the private sector. I think that’s what the country needs right now.”

Gingrich fired back in an interview following a town hall meeting tonight at the Newberry, S.C., Opera House.

“You’re talking to a guy who was dead in June. I’m now being attacked by the former frontrunner,” he exulted.

He also defended his economic experience. “I would point out as a matter of fact, having participated in the development of supply-side economics with (former Rep. Jack) Kemp, having campaigned with Reagan on it in 1980, having helped pass it in ‘81 and having gone thorugh the recovery in the ‘80s and having 11 million jobs created over four years as speaker, I may have some knowledge of the economy.”

In the interview, Romney used a line of attack similar to the one he employed against Texas Gov. Rick Perry when he shot up in the polls in August and September.

With his remarks to Baier, Romney signaled that he is threatened by Gingrich’s standing and that he may mount a more aggressive posture. After his campaign struggled all summer, Gingrich was buoyed by strong debate performances and now sits with Romney atop most state and national polls.

On Sunday, Gingrich won the coveted endorsement from the New Hampshire Union Leader, the largest newspaper in the first-in-the-nation primary state where Romney is thought to be the heavy favorite.

Romney was testy through much of the interview with Baier, which was filmed early Tuesday morning inside a Cuban food wholesaler in Miami just before Romney’s campaign rally there.

Baier peppered Romney with questions about his inconsistencies over the years on key issues like climate change, abortion rights, immigration and gay marriage. Romney rejected the premise altogether.

“Well, Bret, your list is just not accurate,” Romney said. “So, one, we’re going to have to be better informed about my views on issues. My view is you can look at what I’ve written in my book [“No Apology”]. You can look at a person who has devoted his life to his family, to his faith, to his country. And I’m running for president because of the things I believe I think I can do to help this country.”

Romney acknowledged that he parts company with other Republicans on a number of issues, but cast that as a virtue, saying his refusal to change positions on his Massachusetts health care overhaul is principled.

“I’m not a carbon copy of all the people in my party,” Romney said. “This whole stream of thought that you began with, which is will you say anything to get elected, if that were the case, would I still be defending Massachusetts health care? It’s by far the biggest challenge I have in the primary race. And if I were willing to say anything to get elected, wouldn’t I just say, ‘Oh, it was a mistake’?”

Romney sounded irritated by the level of scrutiny his evolving positions have received relative to those of other candidates, and singled out a climate change advertisement Gingrich filmed with former House speaker Nancy Pelosi (D-Calif.).

“I’ve watched other people on the stage when they talk about their cap-and-trade policies, they say, ‘Oh, that was a mistake,’” Romney told Baier. “When someone says, ‘Oh, I did this ad on global warming, that was a mistake.’ So they’ve just brushed it aside.”

“I’m standing by what I did in Massachusetts,” Romney added. “I’m not trying to dust it aside. I’m absolutely firm that it was the right thing for our state. I’ll defend that and I understand it has political implications. And if it keeps me from winning a primary, so be it. But that happens to be the truth.”

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