COLUMBIA, S.C. – Former House Speaker Newt Gingrich stormed to an upset win in the South Carolina primary Saturday, dealing a sharp setback to former front-runner Mitt Romney and scrambling the race for the Republican presidential nomination.

“Thank you, South Carolina!” a jubilant 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,” his tweet said.

Romney was unbowed. He vowed to contest for every vote in every state and unleashed a double-barreled attack on President Obama and Gingrich.

Referring to 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 night’s primary winner’s name.

Former Pennsylvania Sen. Rick Santorum and Texas Rep. Ron Paul trailed badly in the South Carolina voting. Returns from 30 percent of the state’s precincts showed Gingrich gaining 41 percent of the vote, to 26 percent for Romney. Santorum had 18 percent and Paul 13.

Exit polling showed Gingrich, the former House speaker, leading by a wide margin among the state’s heavy population of conservatives, tea party supporters and born-again Christians.

For the first time all year, Romney trailed among voters who said they cared most about picking a candidate who could defeat Obama. Gingrich was ahead of the field for those voters’ support.

Since Ronald Reagan in 1980, every Republican contender who won the primary has gone on to capture the party’s nomination.

Nearly two-thirds of voters Saturday said they are born again or evangelical Christians, and they backed Gingrich over Romney by 2-1 also.

More telling, 6 in 10 voters said it was important that their candidate share their religious beliefs. Nearly half of such voters backed Gingrich, while only about 1 in 5 chose Romney or Santorum.

About 8 in 10 voters said they were very worried about the direction of the country’s economy, and they picked Gingrich over Romney by about a 4-3 edge.

South Carolina’s unemployment rate of 9.9 percent is worse than the national average, and the exit poll provided evidence of the state’s economic pain.

About three in 10 said someone in their household has lost a job in the past three years.

And about 1 in 5 said they are falling behind financially – about double the proportion who said so in exit polling in the state’s 2008 GOP presidential primary.

There were 25 Republican National Convention delegates at stake in South Carolina, but political momentum was the real prize with the race to pick an opponent to Obama still in its early stages.

Santorum, a former Pennsylvania senator, pinned his South Carolina hopes on a heavy turnout in parts of the state with large concentrations of social conservatives, the voters who carried him to his strong showing in Iowa.

Paul had a modest campaign presence here after finishing third in Iowa and second in New Hampshire.

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.