U.S. presidential rivals Mitt Romney and Newt Gingrich battled to win last-minute supporters on Saturday in a South Carolina primary that could reshape the Republican nominating contest.
The race in the conservative southern state, known for gloves-off politics, has been upended in recent days as the two candidates have tried to portray each other as untrustworthy.
Gingrich, who has surged in popularity in South Carolina in recent days, has attacked Romney's business record and reluctance to release personal tax information, while Romney has pointed to Gingrich's past ethics lapses.
Yet voters said they were overwhelmingly focused on fixing the sluggish economy and finding the strongest candidate to defeat Democratic President Barack Obama. Some 78 percent said they were very worried about the economy and 45 percent said that the most important trait in a candidate was the ability to beat Obama, according to exit polls released by CNN.
Romney, the former governor of Massachusetts, must win the conservative southern state to preserve his front-runner status in the race to determine the Republican Party's challenger to Obama in the November 6 election.
Gingrich's recent rise has slowed Romney's momentum.
A victory by the former speaker of the House of Representatives could prolong the state-by-state Republican nominating battle and give Obama's re-election campaign a boost as his would-be Republican opponents beat each other up.
South Carolina is the third contest in the Republican nomination battle. Former U.S. senator Rick Santorum was the winner in Iowa on January 3 and Romney won in New Hampshire on January 10, with Gingrich faring poorly in both those states.
Polling in South Carolina closes at 7 p.m. eastern/0000 GMT.
A new poll conducted by the American Research Group showed Gingrich leading Romney 40 percent to 26 percent among likely voters in South Carolina. The margin of error in the survey, conducted Thursday and Friday, was 4 percentage points.
Romney, slipping in recent polls after coming under intense criticism from Gingrich and other rivals, seemed to acknowledge he might not lock up the nomination this weekend.
We've got a long way to go. So come join us in Florida, in Nevada, Michigan, Colorado, he said, standing on a chair in a crowded restaurant, Tommy's Country Ham House, and referring to Gingrich as a Washington insider.
The next contest after South Carolina is the Florida primary on January 31.
Gingrich, a southern conservative who has called Romney a Massachusetts moderate, showed up at the same restaurant shortly after Romney left. Where's Mitt? he taunted. I don't think they have New England clam chowder on the menu. Clam chowder is popular in Massachusetts.
Romney may be helped if the South Carolina conservative vote is splintered among Gingrich, Santorum and U.S. congressman Ron Paul, who is known for his libertarian views.
Voter turnout, which weather could influence, will also be key. A tornado watch was in effect for much of the state and severe thunderstorms were on the forecast.
Gingrich's latest surge in opinion polls has created a different kind of storm. If he wins the state, it would mean that three different candidates will have won the first three Republican presidential nomination contests.
With strong debate performances, the thrice-married Gingrich has fended off publicity about his turbulent marital history and painted himself as the more conservative candidate with experience as a reformer. On Thursday, he rejected his second wife's accusation that he had asked her for an open marriage while he was having an affair with another woman in the 1990s.
He's a bulldog, and I'm tired of the namby-pambiness, said
Caron McBreairty, 53, who voted for Gingrich. I went with the good debater.
Kim Woods, 53, a photographer, said Gingrich's Washington experience - which Romney has belittled - was an asset. He's been in D.C. He's been in the political realm. He can get some things done, she said.
In an attack that resonated in Iowa, Romney highlighted Gingrich's ties to mortgage giant Freddie Mac and criticized his time in the nation's capital. His campaign has also highlighted Gingrich's $300,000 fine due to ethics lapses while serving as House speaker 15 years ago.
If people think that someone who spent the great majority of their life in Washington is what we need to change Washington, I'll be surprised, he said.
Obama, who does not face a primary challenger, will have his turn in the spotlight on Tuesday with his State of the Union address. In a message sent to supporters on Saturday, he signalled the speech would include a partisan call for a return to American values of economic fairness.
On the Republican side, however, with two other candidates trailing in the polls, the primary looks like a straight fight between Gingrich and Romney, with Paul and Santorum trailing.
Newt has positioned himself as the 'anti-Romney' and this strategy has played well in South Carolina, said Republican strategist Ron Christie.
The question is whether this has broader appeal in more diverse states. As for Romney, this sparring will serve him well for the general election should he become the Republican nominee.
Fueled by a grudge that has become almost personal, Gingrich has sown seeds of doubt among Republicans who were beginning to see Romney as the inevitable nominee to face Obama after his strong showings in Iowa and New Hampshire.
Romney has stumbled, acknowledging in the last week he pays a much lower tax rate than many Americans and struggling to answer questions about a planned release of tax records. Romney is among the richest men ever to run for the U.S. presidency and his stewardship of the private equity firm Bain Capital has been criticized by Gingrich and others.
Romney's campaign tried to turn the tables and ask for more information about ethics violations for which Gingrich was sanctioned in the U.S. Congress in the 1990s. It noted that Saturday was the 15th anniversary of Gingrich being reprimanded by fellow lawmakers.
Animosity between the two has been festering since December, when a group supporting Romney launched a blitz of negative TV ads in Iowa that effectively ruined Gingrich's campaign there.
He has hit back by attacking Romney's business record.
The fight has been bruising in South Carolina, a conservative state with a history of dirty politics.
Romney's team is playing up his family background as a contrast to Gingrich.
The winner of South Carolina's Republican presidential primary has gone on to win the party's nomination in every presidential election since 1980. Romney's path to the nomination would be nearly clear if he can clinch the state on Saturday.
Regardless of what happens in South Carolina, this is still Mitt Romney's race to lose, and I don't think he's going to lose it, said Republican strategist Todd Harris, adding that Gingrich had failed repeatedly to capitalize on his strengths.
Romney's campaign is like a slow and methodical game of chess. Newt's is more like Chutes and Ladders.