Just five days ago, Mitt Romney said if he could do one thing over about his campaign, he would spend less time attacking his opponents and more time talking about President Barack Obama.

"I would go back and take every moment I spent talking about one of the guys on the stage and spent that time talking about Barack Obama," Romney said Thursday at a presidential debate sponsored by CNN. "The right course for America is to return to our fundamental principles, and I would be talking about that more, and probably about my colleagues less--because frankly, any one of them would be a better president than the one we've got."

That was before Romney lost by double-digits to Newt Gingrich in South Carolina. Over the last 48 hours, Romney has gone from barely mentioning his rivals on the stump or in news interviews to launching an all-out assault on Gingrich, portraying him as an erratic and unethical leader who would be dangerous for the party.

Speaking to reporters this morning before tonight's NBC debate in Tampa, Romney warned of an "October surprise a day" if Gingrich wins the Republican nomination, citing ethics investigations dating back to Gingrich's days as speaker of the House. Romney also hammered Gingrich for his consulting work after he left office, calling on the former lawmaker to release records detailing his work for Freddie Mac and on behalf of clients lobbying for health care and Medicare reform.

"Let's see the records from the ethics investigation. Let's see what they show. Let's see who his clients were at the time he was lobbying Republican congressmen for Medicare Part D. Was he working or were his entities working with any health care companies that could have benefited from that?" Romney said. "That could represent not just evidence of lobbying but potentially wrongful activity of some kind. And finally, let's also see the relationship with Freddie Mac and the work product of Freddie Mac. Let's have full disclosure of what's going on."

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Romney did not specify what kind of "wrongful activity" he suspected on Gingrich's part, and the Romney campaign did not immediately respond to a request for comment from Yahoo News.

Romney derided Gingrich's defense that he was not formally registered as a lobbyist with the House or Senate.

"Saying that Newt Gingrich is a lobbyist is just a matter of fact. He indicates that he doesn't fall within the narrow definition of lobbyists that he might have in mind. But if you're working for a company, getting paid for a company through one of your many entities and then you're speaking with congressmen in a way that would help that company, that's lobbying," Romney insisted. "If it walks like a duck and quacks like a duck, it's a duck."

In a subsequent conference call, Romney campaign surrogates said Gingrich was not fit for office.

And the campaign unveiled a new TV ad about Gingrich's work for Freddie Mac, set to begin airing Monday in Florida. The ad mocks Gingrich's claim that he was hired as a historian by the company and implies that he profited off the suffering of Floridians hit hard by the housing crisis.

"While Florida families lost everything in the housing crisis, Newt Gingrich cashed in," the ad says.

Playing a clip of Gingrich saying he worked as a "historian," a narrator intones, "A historian? Really?"

The ad also mentions Gingrich's ethics problems and says he "resigned from Congress in disgrace."

In response, the Gingrich campaign organized its own conference call with former Rep. J.C. Watts, a top Gingrich surrogate, who defended Gingrich's claims that he didn't work as a lobbyist, calling Romney's attacks "silly."

"I guess technically, some might see it as splitting hairs, but Newt Gingrich was not walking the halls of the House and Senate, going from Republican and Democrat," Watts said. "He was never doing the hand-to-hand combat lobbying or consulting, whatever you want to call it."

"Beating up Newt Gingrich for consulting ... I think that's about like saying let's beat up Michael Jordan for being a great basketball player," Watts went on to say. "You want somebody that's been there, done that."

Romney's attacks on Gingrich are not likely to let up, especially as the candidates meet on stage to debate Monday night in Tampa and again on Thursday in Jacksonville.

In recent days, the former Massachusetts governor has sought to recast his candidacy as someone from outside Washington fighting party insiders like Gingrich—a theme that likely to dominate Romney's message in Florida and throughout the rest of the primaries.

Florida House Speaker Will Weatherford, who has endorsed Romney in the race, raised the issue in a conference call Monday, telling reporters it is difficult to believe Gingrich could be an agent of "change" in Washington, given his long history there.

"We need principled leaders, not political opportunists," Weatherford said.

He laughed at Gingrich's claim of working as a historian for Freddie Mac, saying that he didn't believe anybody in the state would buy that excuse.

"$1.6 million for a history lesson?" he said. "He should have been giving them a math lesson."

Chris Moody contributed to this report.

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