CHARLESTON, S.C. — A reduced field of four candidates took to the stage in Charleston for the CNN Republican debate Thursday night, with Mitt Romney and Newt Gingrich forced to respond to recent attacks on their respective records.The seventeenth debate of the cycle — held at the North Charleston Coliseum — began with CNN moderator Jon King asking Gingrich about an explosive new ABC News interview in which his second wife, Marianne Gingrich, said the former House Speaker had petitioned her to accept an “open marriage” in 1999 after admitting to a six-year affair with Callista Bisek, now his third wife. EPA Republican presidential candidates Mitt Romney (L) and Newt Gingrich trade opinions during the CNN Southern Republican Presidential Debate at the North Charleston Coliseum in North Charleston, South Carolina. Gingrich vehemently denied the allegation and chastised the network for beginning the debate with that topic.”The story is false,” he said, adding that he was “astounded that CNN would take trash like that and use it to open a presidential debate.” He was greeted with loud applause from the audience as he decried the “destructive, vicious, negative nature of much of the news media.”Asked for his reaction to the story, Romney said simply, “let’s get on to the real issues, that’s all I’ve got to say.”The debate capped a tumultuous day on the campaign trail that saw Texas Gov. Rick Perry drop out of the race and endorse Gingrich, who has re-emerged as Mitt Romney’s chief rival for the nomination, despite disappointing fourth-place finishes in Iowa and New Hampshire.Romney was asked to defend his tenure as CEO of private equity fund Bain Capital early on in the debate. He noted that the companies he invested in had created 110,000 jobs, saying, “capitalism works, free enterprise works,” and later adding that “there’s nothing wrong with profit, by the way.”Asked again if he would release his tax records, Romney said he would release his 2011 tax return in April but did not commit to releasing all his returns from previous years, an answer which brought some boos from the crowd.”I pay full taxes, I’m honest in my dealings with people,” he said.”I’m not gonna apologize for being successful,” he continued, noting that Democrats would inevitably go after him because of his vast personal fortune, estimated to be in the ballpark of $250 million. “I didn’t inherit money from my parents,” he told the crowd. “What I have, I earned.”Earlier in the week, he told reporters that his personal wealth would probably be subject to an effective tax rate of 15 percent, below that of many average Americans who derive their earnings through income and not investments.Romney, who has made his private sector experience central to his argument that he is the best equipped candidate to take on President Barack Obama in the general election, said that he would staunchly defend the capitalist system and would “stuff it down” the president’s throat in November and “point out that it is capitalism and freedom that makes this country strong.”The former Massachusetts governor, who appeared to be in cruise control after winning the first two contests in Iowa and New Hampshire, suffered a setback Thursday morning when the Iowa Republican Party announced that the final certified caucus results showed that former Pennsylvania Sen. Rick Santorum, and not he, had actually received the most votes in the Hawkeye State.The news — which on another day may have given some much-needed momentum to Santorum — was instead drowned out by Perry’s exit and subsequent endorsement and the Marianne Gingrich interview.Santorum — who with Texas Rep. Ron Paul made up the four debaters — attacked both Romney and Gingrich over health care, noting that despite their tough talk about repealing Obamacare, both had previously supported the individual mandate.”Governor Romney tells a very nice story,” Santorum said, before reminding debate viewers that his rival’s health care overhaul in Massachusetts had been an “abject failure” and was the basis of Obama’s national model.Santorum also went after Gingrich, for suggesting that he drop out of the race so that conservatives could rally around his candidacy.”Grandiosity has never been a problem with Newt Gingrich,” he said, reminding the audience that he had outperformed the former speaker in both Iowa and New Hampshire.”You’re right, I think grandiose thoughts, this is a grandiose country,” Gingrich shot back.A Rasmussen Reports poll released prior to Thursday’s debate showed that Gingrich now leads in the Palmetto State, gaining the support of 33 percent of voters compared to 31 percent for Romney.Since 1980, the winner of the South Carolina Republican primary has always gone on to win the nomination.