Former House speaker Newt Gingrich scored an easy victory Saturday in the South Carolina primary, blowing a hole in Mitt Romney’s aura of inevitability.

The 12-point win represented a swift and extraordinary turnaround in Gingrich’s fortunes — thanks largely to strong performances in two debates. In those forums, he issued a stirring appeal to the state’s strident conservatism, convinced its voters he would be a formidable opponent against President Obama and threw Romney off his stride.

“We don’t have the kind of money that at least one of the candidates has,” Gingrich said in his victory speech in Columbia, referring to Romney. “But we do have ideas, and we do have people and we proved here in South Carolina that people power with the right ideas beats big money.”

He also peppered his speech with dismissive references to “elites” in the media and in Washington and New York — a sign that he intends to continue the truculently populist tone that resonated with voters in South Carolina.

After disappointing distant finishes in the Iowa caucuses and the New Hampshire primary, Gingrich had limped into South Carolina more than 10 points down in most polls. So battered was his candidacy that Gingrich himself had conceded that his campaign might be over if he failed to turn in a strong performance.

His victory not only changes the near-term dynamic of this presidential campaign but also defies political history. South Carolina is known as a firewall for the GOP establishment in presidential contests, traditionally extinguishing the hopes of insurgent candidates such as Gingrich.

This year also marks the first time that a different Republican candidate has won each of the first trio of contests — still further evidence of how unsettled and dissatisfied the party’s voters are in a year when they are anxious to unseat a vulnerable incumbent president.

Since 1980, every South Carolina GOP primary winner has gone on to win the party’s nomination. But how far this victory will carry Gingrich remains very much in question. Although Romney has yet to win over the Republican activist base, he has by far the most formidable financial resources and organization. Those give him a substantial edge as the contest moves next to the vast state of Florida, which holds its primary Jan. 31.

And in his concession speech, Romney — who has until now trained most of his fire on Obama — signaled that he will be taking a harder line against Gingrich as the contest goes forward.

“The choice within our party has also come into stark focus. President Obama has no experience running a business and no experience running a state. Our party can’t be led to victory by someone who also has never run a business and never run a state,” Romney said. “Our president has divided the nation, engaged in class warfare and attacked the free-enterprise system that has made America the economic envy of the world. We cannot defeat that president with a candidate who has joined in that very assault on free enterprise.”

Romney was incorrect in his assertion that Gingrich has never run a business. After leaving Congress in 1999, Gingrich built a successful conglomerate of them, largely drawing upon his own talents as a speaker, consultant and writer.

That “assault on free enterprise” to which Romney referred was Gingrich’s continuing criticism of Romney’s record as a corporate turnaround specialist, which Gingrich has described as “exploitive” because it often involved adding debt to the companies he acquired and laying off workers.

Even some of Gingrich’s allies have been uncomfortable with that line of attack, saying it echoes the anti-business rhetoric of the Occupy Wall Street movement and may be turned by Democrats into ammunition against Romney, who remains the favorite for the nomination.

Gingrich’s team acknowledges that he suffered some self-inflicted damage by taking that hard line against Romney in New Hampshire.

In addition to regaining his footing, strategists say the former speaker confronted two major challenges in South Carolina: He had to convince voters here that he could take on Obama in the fall, and he had to stir doubts about Romney’s electability, character and conservatism.

How well he succeeded at both of those goals was apparent in the exit polls. Unlike in Iowa and New Hampshire, Gingrich came out ahead of Romney among those voters who said that an ability to win in November was the quality they were looking for most in a candidate.

As Gingrich took the stage Saturday night to give his victory speech, his supporters chanted: “Newt can win!”

In another sign of how he had changed the dynamic, Gingrich outpolled Romney 4 to 3 among voters who rated the economy as their greatest concern — even though economic expertise has been one of Romney’s chief selling points.

It was not the first resurrection that Gingrich has experienced during the course of the campaign. His operation collapsed last summer, when much of his staff quit over disagreements about his unconventional strategy. And then when he rebounded in the late fall, an outside political organization backing Romney unleashed millions of dollars worth of ads against Gingrich in Iowa that helped deflate his candidacy there.

Things began to turn his way again in the first of two debates last week. When Fox News Channel moderator Juan Williams asked whether Gingrich’s characterization of Obama as a “food stamp president” carried racial overtones, the former speaker brought the Myrtle Beach audience to its feet with a denunciation of political correctness and a passionate defense of the work ethic.

“The debate Monday night may have been a game changer,” Gingrich said in an interview with The Washington Post two days later.

However, the week leading up to the primary had more than its share of unexpected twists.

Gingrich received a boost when one of his rivals, Texas Gov. Rick Perry, abruptly dropped out of the race and endorsed him. Gingrich also picked up the backing of tea party heroine Sarah Palin, the former governor of Alaska.

Romney was also dealt a setback, at least in bragging rights, when the Iowa Republican Party reversed its earlier determination and declared that former senator Rick Santorum (Pa.) had won the Jan. 3 caucuses. That switch may ultimately prove to be a blessing for Romney because it gives Santorum, who placed a distant third in South Carolina, a rationale to remain in a race in which he is fighting with Gingrich over conservative voters.

However, Gingrich also found himself on the defensive, when his second wife, Marianne, accused him in interviews with ABC News and The Post of wanting an “open marriage” in which he could divide his affections between her and the mistress who became his third wife.

When asked about those allegations during Thursday night’s debate, Gingrich turned the tables on moderator John King of CNN.

Exit polls suggest the jujitsu was successful. Gingrich fared well among both evangelical voters and women — two groups whose support might have been shaken by his ex-wife’s interview.

Meanwhile, Romney stumbled in the debates, particularly in his convoluted explanations of why he has not yet released his tax returns, which served as a reminder of his wealth.

Overall, the debates proved to be a decisive factor in South Carolina.

In preliminary exit polls, more than half of voters say they decided in the closing days of the campaign, and Gingrich held a roughly 20-point lead in this group. Romney matched Gingrich among those who decided earlier.

Gingrich’s strongest support came from those who said the debates had been the “most important factor” in making their choice.

“It’s not that I am a great debater, it is that I articulate the deepest-felt values of the American people,” Gingrich said in his victory speech.

Two more debates are scheduled for this week in Florida, one Monday and another Thursday.

Though Romney’s participation in those debates had been in question, his campaign confirmed Saturday that he will appear at both — which was welcome news to Gingrich’s team.

Another factor contributing to Gingrich’s success was the outside spending by a “super PAC” supporting his candidacy. Shortly before the South Carolina contest, it received a $5 million contribution from Las Vegas casino magnate Sheldon Adelson.

Going into Florida, “we will raise a boatload of money, and then we will do what we did in South Carolina,” said Rick Tyler, a former Gingrich aide who runs the Winning Our Future super PAC.

Polling director Jon Cohen contributed to this report.