Kirsten Luce for The New York Times  Newt Gingrich's bus pulled into Bluffton, S.C., on Thursday. His wife, Callista, is at right.  CHARLESTON, S.C. — A moment that Newt Gingrich had long been hoping for and one that he had long been dreading collided on Thursday as a new opening for him to rally conservatives around his candidacy was suddenly complicated when the second of his three wives stepped forward to say he had asked for an “open marriage.”  As Gov. Rick Perry of Texas dropped out of the Republican presidential race and threw his support behind Mr. Gingrich, he declared, “Newt is not perfect, but who among us is?” But after belatedly discovering that he had won the Iowa caucuses, Rick Santorum, Mr. Gingrich’s rival for the role of conservative alternative to Mitt Romney, made a pointed appeal to evangelical voters, calling himself someone who “walks the walk and talks the talk.”  Two days before the South Carolina primary, the Republican campaign was upended by a torrent of developments from dawn to dusk that left Mr. Romney unsure of his footing. He made a congratulatory call to Mr. Santorum after the Republican Party in Iowa wiped out his eight-vote margin and put Mr. Santorum ahead, but Mr. Romney’s aides were so skittish that they insisted it was not a concession.  Mr. Gingrich was at center stage when the candidates opened their final debate before the primary, angrily denouncing questions about whether he had sought an open marriage and then aggressively taking on Mr. Romney and the other remaining candidates in a raucous confrontation about policy, conservative credentials and electability.  The cascading events shook the perception of inevitability surrounding Mr. Romney’s march toward the nomination and left Mr. Gingrich with the simultaneous challenges of holding off Mr. Santorum, dealing with the baggage of his past and convincing Republicans that he is the most reliably conservative and electable candidate.  “I have no question that Newt Gingrich has the heart of a conservative reformer and the ability to rally and captivate the conservative movement,” Mr. Perry said, a testimonial aimed at undercutting Mr. Romney’s argument that he is ideologically consistent and the party’s best hope of defeating President Obama.  The question looming over the race was whether conservatives wary of Mr. Romney would follow Mr. Perry’s lead and coalesce behind Mr. Gingrich or if they would remain split among Mr. Gingrich, Mr. Santorum and Representative Ron Paul of Texas.  Mr. Perry’s decision to leave the race and endorse Mr. Gingrich eclipsed what was shaping up as a big day for Mr. Santorum. News of Mr. Santorum’s newly minted victory in Iowa, by a margin of 34 votes, was drowned out almost as soon as it broke.  But Mr. Santorum’s campaign was hoping to capitalize on the reminders of Mr. Gingrich’s marital history that were pushed to the forefront of the race when his second wife, Marianne Gingrich, told ABC News that Mr. Gingrich had once asked her to enter into an open marriage arrangement so he could continue seeing Callista Bisek, a Congressional aide whom he later married.  As he campaigned in South Carolina, trying to seize upon the fresh endorsement from Mr. Perry, Mr. Gingrich tried to change the subject. He blamed ABC News for broadcasting an interview that he called “tawdry and inappropriate,” but he did not directly respond to the account from his former wife, to whom he was married for 18 years.  “I’m not going to say anything about Marianne,” Mr. Gingrich told reporters, referring questions to his two adult daughters from his first marriage. “I’m not getting involved.”  The Santorum campaign, which is aggressively courting evangelical voters across South Carolina, received the endorsement on Thursday of James C. Dobson, an elder statesman of the evangelical movement.  At a weekend gathering of religious leaders in Texas, Dr. Dobson said Mr. Santorum’s wife would make a better first lady than Callista Gingrich. Seeking to explain his views in a letter to Politico, he said it was “known that Callista Gingrich was his mistress for years.” He drew a comparison, saying, “Karen Santorum would make a great first lady.”  Mr. Santorum, a former Pennsylvania senator, said he was the only candidate still in the race who cared deeply about socially conservative issues. He warned voters that Mr. Gingrich would “push them aside and focus on other things.”  Mr. Santorum did not discuss the interview with Mr. Gingrich’s ex-wife. But Michael Biundo, the Santorum campaign manager, said, “If you’re supporting Rick Santorum, you’re never going to have to worry about opening the newspaper and being surprised at what you see.”  Mr. Gingrich welcomed the endorsement of Mr. Perry, and tried to use it to persuade conservative voters to join his candidacy. But a critical megaphone for news — talk radio — was consumed with a debate over whether his alleged request for an open marriage would harm him. It should not, said Rush Limbaugh, because he had at least asked permission.  Reporting was contributed by Trip Gabriel from Bluffton, S.C.; Katharine Q. Seelye from Mount Pleasant, S.C.; Erik Eckholm from Greenville, S.C.; and Ashley Parker from Charleston, S.C.
Newt Gingrich got a big lift for his campaign when Rick Perry dropped out of the race, but there was also a damaging claim from an ex-wife.