MANCHESTER, New Hampshire (Reuters) - Even as the Republican presidential candidates fight it out in New Hampshire, a bigger showdown is looming in South Carolina, a conservative state with a history of nasty politics and picking winners.
The state's primary on January 21 - 11 days after New Hampshire - could be the last stand for conservatives hoping to stop more moderate frontrunner Mitt Romney, who is likely to charge into South Carolina off consecutive wins in Iowa and New Hampshire, where he has a big lead in polls.
A Romney win in South Carolina would essentially wrap up the nomination early, but a victory by a conservative like Rick Santorum would give the Republican Party's right-wing a long-sought savior to rally around in a race that moves on to Florida and other states.
"South Carolina is where the anybody-but-Romney forces hope to finally find their standard-bearer," said Republican strategist Tucker Eskew, who is from South Carolina. "It's the killing ground and birthing ground for presidential hopes."
The state's strategic importance was evident on Thursday when Romney left New Hampshire for a 24-hour visit to South Carolina to campaign with Governor Nikki Haley and Arizona Senator John McCain, who have endorsed him.
Texas Governor Rick Perry, who briefly considered dropping out of the race after a poor fifth-place showing in Iowa, also headed to South Carolina to make a pitch to his fellow Southerners and conservatives.
"South Carolina is a place that I feel very comfortable," Perry told reporters in Iowa on Wednesday, adding that he looked forward to leaving "quirky" Iowa and talking to "real Republicans" in South Carolina.
South Carolina, which has backed the Republican White House winner every year since the primary's inception in 1980, has a history of ugly and decisive primary battles.
"If you like your politics to be Sunday-school nice and polite, this isn't the place for you," said Republican strategist David Woodard, who teaches at Clemson University in South Carolina.
The brutal 2000 fight between George W. Bush and McCain, which featured a rash of anonymous anti-McCain smears, was vital in Bush's march to the White House. In 2008, McCain beat back a challenge from rival Mike Huckabee that helped him clinch the nomination.
As the moderate former governor of Massachusetts, Romney faces a tough challenge in South Carolina even if he does ride a wave of momentum after New Hampshire. He was a distant fourth in the state in 2008 with 15 percent.
Romney has had trouble winning over conservatives unhappy with his Massachusetts healthcare plan that became a model for Obama's federal overhaul and with his past support for abortion rights.
"They see this (South Carolina) as maybe the last place where they can stop him," McCain said of conservatives during an interview with Reuters on Thursday as he campaigned with Romney.
South Carolina Republican primary voters in 2008 were overwhelmingly conservative and religious, with exit polls showing nearly two-thirds attended church at least once a week and seven in 10 believed abortion should be illegal.
But about 500,000 Republicans are expected to vote in South Carolina's contest, compared to 122,000 in Iowa, making the state a more diverse and representative slice of party voters.
"This state has a mix of Republican voters unlike any other, and it's made for retail politics," said former state party chairman Katon Dawson, now Perry's state chairman.
South Carolina's unemployment rate of 9.9 percent - higher than the national average and worse than all but seven other states - could make voters more receptive to Romney's pitch that as a former businessman he knows how to create jobs.
Perry's decision to stay in the race also should benefit Romney, helping to keep the conservative vote fractured between Perry, Santorum, former House speaker Newt Gingrich or U.S. congressman Ron Paul.
"You are going to have a bunch of people splitting up the conservative vote like in Iowa, and that gives Romney a chance to put together a coalition that could win," said South Carolina-based strategist Jim Dyke. "If Romney wins, he can close the deal."
No South Carolina polls have been taken since mid-December, but the most recent showed Gingrich with a double-digit lead over Romney. Those polls were taken before he fell back to the pack under a wave of negative attack ads, but showed the thirst for an alternative to Romney in the state.
They were also taken before Santorum's climb in Iowa, where the former U.S. senator from Pennsylvania virtually tied Romney with a late surge after a largely grass-roots campaign operated on a shoestring budget.
That lifted Santorum into a position to bring together the conservative vote. But neither Santorum nor Gingrich have built much of an organization in South Carolina and Romney will be able to flood the airwaves with television ads in the run-up to the vote.
Romney began airing an ad in the state on Thursday criticizing the National Labor Relations Board's recent ruling blocking Boeing from moving a factory to South Carolina.
"Romney's money could be the difference," Woodard said. "Santorum is going to have a lot of work to do to get his message out."
Additional reporting by Steve Holland; Editing by Christopher Wilson