Romney, Gingrich exchange barbs on immigration (AP) - Newt Gingrich cast Mitt Romney as the most anti-immigrant candidate of the four contenders for the Republican presidential nomination in campaign debate Thursday night in Hispanic-heavy Florida. "That's simply inexcusable," the former Massachusetts governor shot back, heatedly denying the accusation. Romney quickly added that Gingrich's campaign had stopped running a radio ad that made the "anti-immigrant charge" after 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 near the beginning of the second debate in four days in advance of next Tuesday's Florida primary. Opinion polls make the race a close one, with two other contenders, former Sen. Rick Santorum of Pennsylvania and Texas Rep. Ron Paul, trailing far behind. But 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 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.