JACKSONVILLE, Fla. (AP) -- An aggressive Mitt Romney repeatedly challenged Republican rival Newt Gingrich Thursday night in the final debate before next week's critical Florida primary, demanding an apology for an ad saying he harbors anti-immigrant sentiments and ridiculing the former House speaker's call to colonize the moon.
"If I had a business executive come to me and say I want to spend a few hundred billion dollars to put a colony on the moon, I'd say, `You're fired,'" Romney declared. That was just one particularly animated clash between two rivals struggling for supremacy in the race to pick an opponent to President Barack Obama in the fall.
Gingrich responded heatedly. "You don't just have to be cheap everywhere. You can actually have priorities to get things done." He said that as speaker of the House he had helped balance the budget while doubling spending on the National Institutes of health.
The debate was the 19th since the race for the Republican nomination began last year, and the second in four days in the run-up to Tuesday's Florida primary. Opinion polls make the race a close one - slight advantage Romney - with two other contenders, former Sen. Rick Santorum of Pennsylvania and Texas Rep. Ron Paul far behind.
Gingrich's upset victory in the South Carolina primary last week upended the race for the nomination, and Romney in particular can ill-afford a defeat on Tuesday.
While the clashes between Gingrich and Romney dominated the debate, Santorum drew applause from the audience when he called on the two front-runners to stop attacking one another and "focus on the issues."
"Can we set aside that Newt was a member of Congress ... and that Mitt Romney is a wealthy guy?" he said in a tone of exasperation.
There were some moments of levity, including when Paul, 76, was asked whether he would be willing to release his medical records. He said he was, then challenged the other three men on the debate stage to a 25-mile bike race.
He got no takers.
In the days since Romney's loss in South Carolina, he has tried to seize the initiative, playing the aggressor in the Tampa debate and assailing Gingrich in campaign speeches and a TV commercial.
An outside group formed to support Romney has spent more than his own campaign's millions on ads, some of them designed to stop Gingrich's campaign momentum before it is too late to deny him the nomination.
With polls suggesting his South Carolina surge is stalling, Gingrich unleashed a particularly strong attack earlier in the day, much as he lashed out in Iowa when he rose in the polls, only to be knocked back by an onslaught of ads he was unable to counter effectively.
Thursday night's first clash occurred moments after the debate opened, when Gingrich responded to a question by saying Romney was the most anti-immigrant of all four contenders on stage. "That's simply inexcusable," the former Massachusetts governor responded.
"Mr. Speaker, I'm not anti-immigrant. My father was born in Mexico. My wife's father was born in Wales. ... The idea that I'm anti-immigrant is repulsive. Don't use a term like that," he added.
At the same time, Romney noted that Gingrich's campaign had been pressured to stop running a radio ad that called Romney anti-immigrant after Florida Sen. Marco Rubio called on Gingrich to do so.
He called on Gingrich to apologize for the commercial, but got no commitment.
About an hour later, Romney pounced when the topic turned to Gingrich's proposal for an permanent American colony on the moon - an issue of particular interest to engineers and others who live on Florida's famed Space Coast.
A career businessman before he became a politician, Romney said: "If I had a business executive come to me and say I want to spend a few hundred billion dollars to put a colony on the moon, I'd say, `You're fired.'"
The audience erupted in cheers, but Romney wasn't finished.
He said the former speaker had called for construction of a new Interstate highway in South Carolina, a new VA hospital in northern New Hampshire and widening the port of Jacksonville to accommodate the larger ships that will soon be able to transit the Panama Canal.
"This idea of going state to state and promising people what they want to hear, promising hundreds of billions of dollars to make people happy, that's what got us into trouble in the first place," Romney said.
Gingrich responded that part of campaigning is becoming familiar with local issues, adding, "The port of Jacksonville is going to have to be expanded. I think that's an important thing for a president to know." He went on to refer to completion of an Everglades project that he did not describe, then noted he had worked to expand NIH while he was speaker.
Gingrich raised questions about Romney's wealth and his investments. "I don't know of any American president who's had a Swiss bank account," Gingrich said. Romney replied that his investments were in a blind trust over which he had no control. "There's nothing wrong with that," declared Romney, who has estimated his wealth at as much as $250 million.
Earlier Thursday, it was disclosed that Romney and his wife, Ann Romney, failed to list an unknown amount of investment income from a variety of sources including a Swiss bank account on financial disclosure forms filed last year. His campaign said it was working to correct the omissions.
Gingrich also failed to report income from his 2010 tax return on his financial disclosure. The former Georgia congressman will amend his disclosure to show $252,500 in salary from one of his businesses, spokesman R.C. Hammond said.
Debating in a state with a large and influential Jewish population, Romney and Gingrich vied to stress their support for Israel rather than criticize one another.
And all four men were quick to name prominent officials of Hispanic descent who deserved consideration for the Cabinet. Gingrich trumped the other three, saying, "I've actually thought of Marco Rubio in a slightly more dignified and central role," an evident reference to the vice presidential spot on the ticket.
Immigration was a recurring theme.
Gingrich said Romney was misleading when he ran an ad accusing the former House speaker of once referring to Spanish as "the language of the ghetto." Gingrich claimed he was referring to a multitude of languages, not just Spanish.
Romney initially said, "I doubt it's mine," but moderator Wolf Blitzer read it aloud and pointed out that Romney, at the ad's conclusion, says he approved the message.
As for immigration policy, it was difficult to discern their differences.
Both men said they want to clamp down in illegal immigration, create programs to make sure jobs go only to legal immigrants and deport some of the 11 million men and women in the country unlawfully.
Gingrich has never said how many illegal residents he believes should be deported, preferring to say that the United States is not going to begin rounding up grandmothers and grandfathers who have lived in the United States for years.
Romney agreed that was the case - and Gingrich said that marked a switch in position.
"Our problem is not 11 million grandmothers," Romney said. "Our problem is 11 million people getting jobs that many Americans, legal immigrants would like to have."
Romney and Gingrich also exchanged jabs over investments in Fannie Mae and Freddie Mac, two mortgage giants that played a role in the national foreclosure crisis that has hit Florida particularly hard.
Gingrich said Romney was making money from investments in funds that were "foreclosing on Floridians."
Romney quickly noted that Gingrich, too, was invested in mutual funds with Fannie Mae and Freddie Mac. He then added that the former House speaker "was a spokesman" for the two. That was a reference to a contract that one of Gingrich's businesses had for consulting services. The firm was paid $300,000 in 2006.