Republican White House hopefuls brawled ahead of South Carolina\'s key vote, with frontrunner Mitt Romney pounding his main conservative threat, Newt Gingrich. With victories in Iowa and New Hampshire already in his pocket, Romney is hoping a win in South Carolina on Saturday will put him on an unstoppable path to being crowned the Republicans\' presidential candidate. But his double-digit lead in opinion polls here appeared to be slipping slightly after Gingrich put up a feisty show in Monday\'s debate. A CNN/Time/ORC survey poll on the eve of Thursday\'s final debate before the primary found Romney leading the former House speaker 33-23 percent among likely voters in the state, just half of his 19-point lead two weeks ago. Fighting back, supporters of Romney, a former Massachusetts governor, branded Gingrich a dangerously erratic leader whose nomination would pave the way for President Barack Obama to win a new term come November 6. Former senator Jim Talent, who served in Congress with speaker Gingrich in the 1990s, on a campaign conference call accused him of saying \"outrageous and destructive\" things that forced others to \"clean up after him\" and helped Democrat Bill Clinton to reelection in 1996. Gingrich practiced \"leadership by chaos\" and would \"help elect another Democrat president,\" added ex-congresswoman Susan Molinari. Romney\'s campaign echoed those themes in a new Internet advertisement and website, both named \"Unreliable Leader,\" that strongly suggested it saw the more conservative former lawmaker as a rising threat ahead of Saturday\'s vote. But Gingrich hit back, defending both his Congress record and crowing that conservatives now were beginning to see him \"as the only realistic chance to stop a Massachusetts moderate.\" \"I think by Saturday we\'ll be ahead, and depending on how many conservatives come home we could be ahead by a pretty comfortable margin,\" he told CNN. He added that under his leadership there were \"four consecutive balanced budgets, $405 billion in debt paid off ... unemployment dropped to 4.2 percent. I\'d say that\'s pretty darned good leadership style.\" Gingrich has worked to position himself as the strongest conservative challenger to Romney, who faces stubborn doubts about his credentials and has yet to rally a majority of Republicans behind him. At a campaign event Tuesday, Gingrich pressed Christian conservative flag-bearer Rick Santorum -- running third in South Carolina -- and Texas Governor Rick Perry to drop their campaigns and throw their lot with him. But neither man appeared poised to heed the call, and time was fast running out for Romney\'s rivals to deny him the nomination. And in what may also dent Gingrich\'s campaign, US media reported late Wednesday that his former wife, Marianne, has given her first television interview with a two-hour exclusive to ABC which could air in the coming days. Gingrich was married when he met Marianne, and then while the couple were still together he started an affair with his third and current wife, Callista.  Romney meanwhile was hitting out at Obama at a rally in Rock Hill after the president blocked construction of a controversial US-Canada pipeline, charging that the Democratic president has not \"taken advantage\" of US energy resources. \"It\'s been a presidency that\'s been as anti-investment, anti-growth, and anti-jobs as we\'ve ever seen,\" he told hundreds of supporters. Romney, dogged with the perception that he is out of touch with Americans, faced a potentially dangerous new front as ABC news reported he had millions of dollars in notorious tax havens like the Cayman Islands. Campaign spokeswoman Andrea Saul confirmed he had money there but said the funds were \"taxed in the very same way they would be\" on US soil. In an interview with Time magazine, Obama also rejected criticism from Republicans over foreign policy, particularly his handling of Iran\'s nuclear ambitions. And he said Republicans seeking to replace him were attempting to win over the party faithful by attacking his foreign policy decisions. \"I think Mr Romney and the rest of the Republican field are going to be playing to their base until the primary season is over,\" Obama said. \"Overall, I think it\'s going to be pretty hard to argue that we have not executed a strategy over the last three years that has put America in a stronger position than it was than when I came into office,\" he added. Next week Obama will tour five swing states crucial to his reelection chances: Iowa, Arizona, Nevada, Colorado and Michigan after his annual State of the Union address to Congress on Tuesday, the White House said.