COLUMBIA, S.C. — Even before Mitt Romney clinched the New Hampshire primary Tuesday, most of the Republican candidates already had turned their eye to the next state in line, South Carolina, which is shaping up to be the key make-or-break test in the party’s presidential nomination marathon.
Former House Speaker Newt Gingrich has called it “the decisive contest,” and Texas Gov. Rick Perry considers it so important that he barely bothered with New Hampshire. Once he decided to continue his campaign after Iowa, he headed straight to South Carolina.
Mr. Romney underscored the importance of South Carolina when he took time out of his New Hampshire schedule to fly down and campaign late last week, and former Sen. Rick Santorum of Pennsylvania sees South Carolina as the best chance to continue his Iowa momentum.
“We view South Carolina as the next big opportunity,” said Stuart Roy, an adviser to the Red, White and Blue Fund, a super-PAC supporting Mr. Santorum’s bid. “Not that New Hampshire isn’t an opportunity, it is — but the field will look significantly different after South Carolina, going into Florida. This is the opportunity to consolidate the field and for the Republican primary race to emerge with a conservative alternative to Mitt Romney.”
Red, White and Blue Fund has committed to spending $190,000 in advertising in the state, joining what is nothing short of a tidal wave of TV ads that are a way for the GOP field to stay on voters’ minds while they have been campaigning up north.
In recent years, South Carolina has been the crucible where nominees were minted, but only after enduring some of the most brutal politicking of the nominating season.
Mr. Romney and Mr. Gingrich are already engaged, with a pro-Gingrich super-PAC planning to spend millions of dollars to attack Mr. Romney over his history at Bain Capital, where he led the venture capital fund that often bought struggling firms and streamlined them, often eliminating jobs in the process.
“The ideal South Carolina fight would be a Georgia conservative versus a Massachusetts moderate,” Mr. Gingrich told reporters Tuesday after a visit to a polling place in Merrimack, N.H.
Meanwhile, Mr. Romney this week added to his own South Carolina ad buy, preparing to fire back.
South Carolina is also looming in importance because, as the primary season extends, some of the candidates have failed to get on the primary ballot in states that will vote in the weeks and months ahead. Former Utah Gov. Jon Huntsman Jr. missed Arizona’s deadline on Monday, meaning he won’t appear on the ballot in a state that borders Utah, where he was governor for more than four years.
His campaign didn’t respond to a request for comment on the Arizona primary, which comes at the end of February.
Meanwhile, only Mr. Romney and Rep. Ron Paul have secured spots on Virginia’s primary ballot, though the other four top candidates are suing to have the qualifying process reopened.
Mr. Gingrich failed to get on Missouri’s ballot, though that state’s Feb. 7 primary is non-binding.
Mr. Paul on Tuesday blasted Mr. Gingrich, Mr. Huntsman and Mr. Santorum, saying that by failing to get on all the ballots, “all three have disqualified themselves from the race for president of the United States.”
For weeks, New Hampshire has been a contest for second place, which has served only to increase attention on South Carolina, where the race has been almost as unpredictable as Iowa. In the end, Mr. Paul bested Mr. Huntsman in second place behind Mr. Romney in New Hampshire.
According to the Real Clear Politics average of polls, Mr. Romney, Mr. Perry, Mr. Gingrich and former candidate Herman Cain have all held leads in South Carolina, and Mr. Santorum is suddenly surging after his near-victory in the Iowa caucuses.
Rallying voters in New Hampshire on Monday, he asked for momentum “so we can go down to South Carolina, kick a little butt down in South Carolina, go down to Florida and keep kicking until we have a strong, principled conservative in the model of Ronald Reagan.”
South Carolina’s Republican primary voters are considered to lean toward the social conservative side of the GOP, which makes the state an attractive battleground for Mr. Santorum and Mr. Perry. It also could be friendly ground for Mr. Gingrich, who while in Congress represented a district in neighboring Georgia, but he has seen a huge lead in state polls evaporate in the past few weeks.
South Carolina should be tougher ground for Mr. Huntsman, who did not compete in Iowa and made his first stand in New Hampshire.
But all eyes will still be on Mr. Romney, the front-runner throughout the campaign and the winner of the first two contests of the race, who has advantages here, including the support of Gov. Nikki Haley and 2008 primary winner Sen. John McCain.
“It’s going to come down, as it always does, to South Carolina,” Mr. McCain said while campaigning with Mr. Romney in South Carolina late last week. “If Mitt Romney wins here, he will be the next president of the United States.”
Mr. Perry has had the state mostly to himself for the last week, and on Tuesday he held three events, campaigning near Charlotte and then heading southwest to campaign near the state capital of Columbia.
Campaigning in Fort Mill, S.C., he criticized Mr. Romney’s time as head of Bain Capital and likened private equity firms to “vultures” that pick apart companies without regard to the jobs lost.
All of the candidates will be on stage for two debates next week, offering another chance to win over voters en masse. For some of the candidates, South Carolina is likely to be the end of the line if they don’t do well.
Mr. Gingrich told the Atlanta Journal-Constitution this week that the state “is the decisive contest.”
• This article is based in part on wire service reports.