Newt Gingrich stormed to an upset win in the South Carolina primary Saturday night, dealing a sharp setback to Mitt Romney and scrambling the race to choose a Republican challenger to President Barack Obama.
The win in the first southern primary marks a dramatic turnaround from Gingrich's poor showing in the first two contests of the Republican presidential campaign. It sets up the likelihood that the race, which Romney once seemed poised to wrap up quickly, could drag on for months.
It also puts Gingrich in a position to establish himself as the true conservative alternative to Romney, who some Republicans see as too moderate. Romney has benefited by having the conservative vote divided among Gingrich, former Sen. Rick Santorum and Texas Gov. Rick Perry, who dropped out Thursday.
Returns from 57 percent of South Carolina's precincts showed Gingrich gaining 40 percent of the vote, to 27 percent for Romney. Santorum had 18 percent and congressman Ron Paul 13.
An exit poll conducted for The Associated Press and U.S. television networks showed Gingrich led by a wide margin among the state's heavy population of conservatives, born-again Christians and supporters of the small-government tea party movement.
The poll by Edison Research involved interviews with 1,577 voters and had a margin of sampling error of plus or minus 4 percentage points.
Gingrich also won the support of voters who said they cared most about picking a candidate who could defeat Obama. Romney has made the claim that he is the most electable candidate a key part of his campaign.
Democrats generally see Romney as the toughest potential rival for Obama, so Saturday's results are likely to please them. They also wouldn't mind a tough, drawn-out primary battle that could weaken the eventual Republican nominee.
Romney, the former governor of Massachusetts, once appeared poised to sweep the first three contests in the Republican race and become the all-but-inevitable nominee.
But what had appeared to be a narrow victory in the first contest, the Iowa caucuses, was later determined to by a narrow loss to Santorum. He easily won the New Hampshire primary, but lost what had been a substantial lead in pre-election polls in South Carolina.
The conservative southern state has long been difficult territory for the former governor of the liberal northeastern state of Massachusetts. He finished fourth there behind the eventual nominee Sen. John McCain in the 2008 race.
Gingrich pressed ahead despite poor showings in Iowa and New Hampshire, boosted by strong debate performances and shrugging off allegations by an ex-wife that he had once asked her for an open marriage so he could keep his mistress.
Santorum's poor showing is a further sign he lacks the organization and money to build on his Iowa victory. Santorum announced shortly after the polls closed that on Sunday he would open his campaign in Florida, site of the next primary. But if he does withdraw at some point, that could benefit Gingrich.
Paul had not been expected to do well in South Carolina. While he has drawn many supporters to his libertarian, small-government message, his call to withdraw U.S. troops from around the world was a tough sell in a state dotted with military installations and home to many veterans.
The vote was the climax to a tumultuous week in which Romney was stripped of his Iowa triumph and contended with uncomfortable questions about his finances, Perry and former Utah Gov. Jon Huntsman dropped out of the race.
Romney, a multimillionaire former venture capitalist, responded awkwardly to questions about releasing his income tax returns, and about his investments in the Cayman Islands.
Addressing supporters Saturday, Romney unleashed a two-pronged attack on Obama and Gingrich.
Referring to criticism of his time at the helm of a private equity firm, Romney said, ``When my opponents attack success and free enterprise, they're not only attacking me, they're attacking every person who dreams of a better future. He's attacking you,'' he told supporters, the closest he came to mentioning Gingrich's name.
Gingrich benefited from a shift in strategy in which he contended that he was the only Republican who could defeat Obama.
He didn't flinch when ex-wife Marianne said in an interview on ABC television that he had been unfaithful for years before their divorce in 1999, and asked him for an open marriage.
Asked about the accusation in the opening moments of a debate Thursday, he unleashed an attack on ABC and debate host CNN and accused the ``liberal news media'' of trying to help Obama by attacking Republicans. His ex-wife's account, he said, was untrue.
The Republican nominee is determined by a series of state-by-state contests to select delegates to the Republican National Convention in late August. Only 25 of the 2,286 delegates were at stake in South Carolina.
Gingrich won at least 15 delegates, with 10 to be awarded. In all, Gingrich has 17 delegates. Romney has 33 delegates.
But South Carolina was more about political momentum than delegates.
As the first primary in a southern state, South Carolina has been a proving ground for Republican presidential hopefuls in recent years.
Since Ronald Reagan won in 1980, every Republican contender who won the primary has gone on to capture the party's nomination.
Already, Romney and a group that supports him were on the air in Florida with a significant ad campaign, more than $7 million combined to date. The state's primary is Jan. 31.
Gingrich, as his victory became apparent, swiftly appealed to supporters for donations ahead of that contest.
``Help me deliver the knockout punch in Florida,'' he tweeted.