The race for the Republican presidential nomination took a turn toward the South Carolina surreal Thursday as Rick Perry dropped out, Newt Gingrich faced stunning allegations from an ex-wife and Mitt Romney struggled to maintain his shaky front-runner's standing.

An aggressive evening debate capped the bewildering day.

Romney was stripped of his Iowa caucus victory Thursday, and then stung by Texas Gov. Rick Perry's withdrawal and endorsement of Gingrich, the former house speaker who was stunningly accused by an ex-wife of seeking an open marriage so he could keep his mistress.

If Canada could vote

If it were up to Canadians, a new poll suggests, Mitt Romney would be the undisputed favourite to face off against Barack Obama in this year's U.S. presidential election. But there's little doubt Canadians would ultimately re-elect Obama.

Fully 59 per cent — including a majority in all regions and across demographic groups — think Obama will be re-elected in November, the Canadian Press Harris-Decima survey suggests.

Mitt Romney is seen as the best challenger by 25 per cent, far ahead of his rivals for the Republican nomination, none of whom scored better than seven per cent. However, 56 per cent had no opinion on who would be the best Republican nominee.

The telephone survey of just over 1,000 Canadians was conducted Jan. 12-15 and is considered accurate to within plus or minus 3.1 percentage points, 19 times in 20.

"Newt's not perfect, but who among us is," said Perry, abruptly quitting the race less than 48 hours before the polls open in Saturday's first-in-the-South primary. He called Gingrich a "conservative visionary who can transform our country."

Perry's decision to end a once-promising candidacy that crashed and burned during previous Republican debates left Romney, Gingrich, former Pennsylvania senator Rick Santorum and Texas Representative Ron Paul to faceoff in yet another debate, this time in Charleston, S.C.

The first question went to Gingrich, who angrily denounced the news media for putting his ex-wife front and centre in the final days of the race. "Let me be clear, the story is false," he said.

'He was asking to have an open marriage and I refused. That is not a marriage.' — Marianne Gingrich, former wife of Newt Gingrich

He was referring to an interview scheduled to air on ABC News in which his former wife, Marianne Gingrich, said he had wanted an "open marriage" so he could have both a wife and a mistress. She said Gingrich conducted an affair with Callista Bistek — his current wife — "in my bedroom in our apartment in Washington" while she was elsewhere.

"He was asking to have an open marriage and I refused. That is not a marriage," she said in excerpts released by the network in advance of the program.

The audience gave Gingrich a standing ovation when he assailed the media, a reaction he can only hope is reflected in voter sentiment on Saturday.

Paul appeared to take a middle course on the issue of Gingrich's behaviour.

"I think our responsibility is sorting facts and fiction," he said. "The people have to sort this out, but I think setting standards [is] very important, and I am very proud that my wife for 54 years is with me tonight."

As the debate proceeded, all four remaining GOP candidates lustily attacked Obama, while Santorum in particular sought to raise his own profile.

'Let me be clear: The story is false.'— Newt Gingrich, on allegations made by ex-wife

Introduced to the audience at the outset, he mentioned his change of fortunes in Iowa, where an evident eight-vote defeat in caucuses on Jan. 3 was belatedly transformed into a 34-vote advantage — though the Iowa Republican Party did not declare a winner.

Santorum jabbed at both Gingrich and Romney, but seemed to focus more attention on the former. If Gingrich is the party nominee, he said, "you sort of have that worrisome moment that something's going to pop. And we can't afford that in a nominee."

In a reflection of the complex political dynamics of the race, first Gingrich and then Santorum challenged Romney over his well-documented switch of position on abortion. Once a supporter of a woman's right to choose, he now says he is "pro-life."

Recent polls, coupled with Perry's endorsement, suggested Gingrich is the candidate with the momentum and Romney the one struggling to validate his standing as front-runner.

The former Massachusetts governor had other challenges in a state where unemployment approaches 10 per cent. He adamantly refused to explain why some of his millions were invested in the Cayman Islands, how much was there or whether any other funds were held offshore.

Under pressure from his rivals to release his income tax returns before the weekend — a demand first made by Perry in a debate on Monday — he told reporters it wouldn't happen. "You'll hear more about that. April," he said, a position he renewed during the debate to jeers from the audience.

Gingrich released his own tax return during the day, reporting that he paid the IRS $613,517 in taxes on more than $3.1 million in income. He also donated about two percent of his income to charity.

His effective tax rate, roughly 31.6 percent of his adjusted income, was about double what Romney told reporters earlier this week he had paid.

The interview with the second of Gingrich's two ex-wives and the evening debate weren't the only political events in the run-up to the Saturday primary. Attack ads for the remaining candidates and their allies ran virtually without letup.

Santorum ran commercials likening Romney to Obama; Gingrich's cast the former speaker as the only candidate who could defeat the president this fall. In a sign of the shifting campaign, Restore Our Future, a political action committee backing Romney, stopped attacking Santorum so it could concentrate its fire on Gingrich.