WASHINGTON (AP) - Strong backing from conservative and religious voters and people fretting about the uncertain economy fueled Newt Gingrich's victory in South Carolina's Republican presidential primary, an exit poll of voters showed Saturday.

The data also showed that for the first time, the former House speaker grabbed two constituencies that his chief rival, Mitt Romney, prided himself in winning in the year's two previous GOP contests in Iowa and New Hampshire. Gingrich bested Romney, the former Massachusetts governor, among the nearly half of voters looking for someone to defeat President Barack Obama this November, 51 percent to 37 percent. And of the 6 in 10 who considered the economy the top issue in picking a candidate, Gingrich prevailed, 40 percent to 32 percent.

Gingrich benefited most from the campaign's final, tumultuous week, the figures showed.

Just over half said they'd chosen a candidate in the last few days, and 44 percent of them backed Gingrich, doubling Romney's support. By 50 percent to 23 percent, the roughly two-thirds who said campaign debates were an important factor also supported Gingrich. There were two GOP debates in South Carolina during the past week, and Gingrich was widely considered to have turned in strong performances in both.

In the campaign's last days, Romney stumbled badly when asked whether he will release his income tax returns and about investments in the Cayman Islands. Gingrich endured an allegation by one of his two former wives, Marianne, that he had asked permission for an open marriage while he was having an affair with the woman who is his current wife, Callista.

That accusation seemed to take only a slight toll on Gingrich.

He was supported by 6 percent of those who said what they most wanted in a candidate was strong moral character, but these voters were less than 1 in 5 of those who showed up Saturday at the polls. Gingrich did better than Romney among women, and fared a bit more strongly among married than unmarried females.

Gingrich won healthy margins among the state's conservatives, who comprise more than 6 in 10 voters in the state, one of the country's reddest. While those results were bad news for Romney, they were even more damaging to Rick Santorum, the former Pennsylvania senator who has been dueling with Gingrich to become the GOP's conservative champion and alternative to Romney.

Gingrich won among conservatives and tea party supporters by nearly 2-1 over Romney. Santorum was slightly behind.

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

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

About 8 in 10 voters they were very worried about the direction of the country's economy, and they picked Gingrich over Romney, 42 percent to 28 percent.

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 3 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 - around double the proportion who said so in exit polling in the state's 2008 GOP presidential contest.

Romney's earlier career heading Bain Capital, a venture capital firm, clearly wounded his prospects. During much of the campaign, Gingrich and others accused Romney and his company of killing jobs in the companies they bought and restructured.

Those blows showed Saturday. According to the exit polls, Gingrich and Romney broke about even among the nearly two-thirds of voters who said they had a positive view of Romney's activities at Bain. But among those who viewed Romney's work negatively, half picked Gingrich and 3 percent backed Romney.

Underscoring how poorly Romney fared in South Carolina, less than 4 in 10 said they could enthusiastically back him should he eventually win the GOP nomination.

Romney's defeat was so sweeping that he lost to Gingrich among voters of every age. The only income group Romney won was people making above $200,000 a year - 1 in 20 of those who voted Saturday. Gingrich also prevailed among voters of every education level except those who have pursued post-graduate degrees, which he split with Romney.

Around two-thirds of voters approved of the job Nikki Haley is doing as governor, which she won with strong tea party support. Haley endorsed Romney, but 7 in 10 tea party backers gave her high marks anyway.

The survey was conducted for AP and the television networks by Edison Research as voters left their polling places at 35 randomly selected sites in South Carolina. The survey involved interviews with 2,381 voters and has a margin of sampling error of plus or minus 3 percentage points.

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Associated Press global polling director Trevor Tompson contributed to this report.