JACKSONVILLE, Florida (AP) - Newt Gingrich cast Mitt Romney as the most anti-immigrant candidate of the four contenders for the Republican presidential nomination in a heated campaign debate Thursday night in Hispanic-heavy Florida.
"That's simply inexcusable" and "repulsive," the former Massachusetts governor shot back, showing newfound emotion and combativeness compared with his earlier debate performances. "My father was born in Mexico. I'm not anti-immigrant."
Romney quickly added that Gingrich's campaign had stopped running a radio ad that made the "anti-immigrant charge" after Cuban-born Florida Sen. Marco Rubio called on him to do so. Romney said to Gingrich concerning the ad, "I think you should apologize for it."
The exchange came in the last Republican debate before next Tuesday's Florida primary, which was seen as a key chance for Gingrich to win a big southern state and stagger the momentum of the better organized and funded Romney campaign.
Opinion polls indicate the race is close, with two other contenders, former Sen. Rick Santorum of Pennsylvania and Texas Rep. Ron Paul, trailing far behind.
Romney's strong debate Thursday night seemed likely to boost his fortunes, setting the stage for a long, grueling battle for months between the two leading Republicans in more primary states in the run-up to the party's nominating convention this summer.
A more aggressive and assured Romney assailed his chief rival, ridiculing Gingrich's call to build costly projects in key political primary states and to colonize the moon.
A career businessman and venture capitalist 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.'"
As charges flew back and forth, Gingrich rebutted any suggestion that he couldn't rein in surging federal spending.
"You don't just have to be cheap everywhere. You can actually have priorities to get things done," Gingrich declared, saying that as speaker of the House of Representatives he had helped balance the U.S. budget while doubling spending on the National Institutes of health.
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.
That seemed unlikely, given the stakes in the primary now five days distant.
Gingrich picked up on the theme quickly, calling on moderator Wolf Blitzer of CNN to let the four candidates discuss the issues.
The audience booed, as if in agreement with Gingrich, but Romney jumped in, saying, "Wouldn't it be nice if people didn't make accusations somewhere else that they weren't willing to defend here."
Moments earlier, Romney and Gingrich had exchanged jabs over investments in Fannie Mae and Freddie Mac, two U.S. 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.
Romney and Gingrich had clashed repeatedly in the first debate of the week, held Monday in Tampa.
Gingrich's unexpected victory in the South Carolina primary last weekend upended the race to pick a Republican opponent for Democratic President Barack Obama in the fall, and Romney could ill afford another setback.
Romney had long been the front-runner, citing his business background as he positions himself as the candidate best able to defeat Obama in an election in which jobs and the economy are the top issues. But he has struggled to win over conservatives who see him as too moderate.
Gingrich, brash and outspoken, has emerged as his main challenger, winning over the Republican base with his sharp-tongued denunciations of Obama and the "elite" news media. But questions have been raised about his personal life and business dealings and some Republicans see him as too erratic to be a viable nominee.
Santorum won the Iowa caucuses, the first test among the candidates.
In the days since his South Carolina loss, Romney 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 Romney's 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.
Gingrich unleashed an attack reminiscent of his rhetoric a month ago when he was being outspent heavily on television and falling sharply in the polls just before the Iowa caucuses.
He accused Romney and Restore Our Future, the independent group, of dishonest ads, and said, "This is the desperate last stand of the old order. This is the kind of gall they have, to think we're so stupid and we're so timid."