COLUMBIA, S.C. -- Former House Speaker Newt Gingrich stormed to an upset victory in the South Carolina primary last night, dealing a sharp setback to former front-runner Mitt Romney and suddenly scrambling the race for the Republican presidential nomination.
"Thank you, South Carolina!" Gingrich tweeted to his supporters. He appealed for a flood of donations for the next-up Jan. 31 primary. "Help me deliver the knockout punch in Florida. Join our Moneybomb and donate now," said his tweet.
Exit polls showed he led among voters who said their top priority was picking a candidate who could beat President Barack Obama -- a group that had preferred Romney in earlier contests in Iowa and New Hampshire.
Romney, the national front-runner until now, was unbowed. He vowed to contest for every vote "in every state" and unleashed a double-barreled attack on Obama and Gingrich.
Referring to Gingrich's criticism of his business experience, 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 the primary winner's name.
Returns from 57 percent of the state's precincts showed Gingrich with 40 percent of the vote to 27 percent for Romney. Former Pennsylvania Sen. Rick Santorum had 18 percent, Texas Rep. Ron Paul 13 percent.
As the first Southern primary, South Carolina has been a proving ground for Republican presidential hopefuls in recent years. Since Ronald Reagan in 1980, every Republican contender who won the primary has gone on to capture the party's nomination.
Based on the vote total, Gingrich won at least 15 of the 25 Republican National Convention delegates at stake and none of the other contenders was yet assured of any.
But political momentum was the real prize, with the race to pick an opponent to Obama still in its early stages.
Already, Romney and a group that supports him were on the air in Florida with a significant television ad campaign, more than $7 million combined to date.
Aides to the former Massachusetts governor had once dared hope that Florida would seal his nomination -- if South Carolina didn't first -- but that strategy appeared to vanish along with the once-formidable lead he held in pre-primary polls.
Romney swept into South Carolina 11 days ago as the favorite after being pronounced the winner of the leadoff Iowa caucuses, then cruising to victory in New Hampshire's first-in-the-nation primary.
But in the sometimes-surreal week that followed, he was stripped of his Iowa triumph -- GOP officials there now say Santorum narrowly won -- while former Utah Gov. Jon Huntsman dropped out and endorsed Romney and Texas Gov. Rick Perry quit and backed Gingrich.
Romney responded awkwardly to questions about releasing his income tax returns, and about his investments in the Cayman Islands. Gingrich benefited from two well-received debate performances while grappling with allegations by an ex-wife that he had once asked her for an open marriage so he could keep his mistress.
By primary eve, Romney was speculating openly about a lengthy battle for the nomination rather than the quick knockout that had seemed within his grasp only days earlier.