COLUMBIA, S.C. (AP) -- Mitt Romney says he's ready for an uphill climb in South Carolina after coasting through New Hampshire. As the Republican presidential contest heads south Wednesday, his rivals are sharpening their attacks and trying to rev up tea partyers and religious conservatives still nervous about the front-runner.

Still, Romney projects a self-assurance that must be wearing on his five opponents. He dismisses much of their criticism as acts of desperation. And he said that while several campaigns can afford to keep the nomination fight going, "I expect them to fall by the wayside eventually for lack of voters."

Despite the rougher tone and tougher ideological terrain ahead, the former Massachusetts governor is hoping to force his opponents from the race by achieving a four-state streak with victories in South Carolina on Jan. 21 and Florida 10 days later.

He posted a double-digit win Tuesday night in New Hampshire after a squeaker the week before in Iowa - making him the first non-incumbent Republican in a generation to pull off the back-to-back feat.

"Tonight we celebrate," Romney told a raucous victory party in Manchester, N.H. "Tomorrow we go back to work."

The way ahead passes through minefields that held him to fourth place in the South Carolina primary when he ran four years ago: Republicans skeptical of his Mormon faith and reversals on some social issues.

All the candidates planned to campaign in the state Wednesday. Romney, former House Speaker Newt Gingrich, ex-Pennsylvania Sen. Rick Santorum, Texas Rep. Ron Paul and former Utah Gov. Jon Huntsman were flying in from New Hampshire. They'll join Texas Gov. Rick Perry, who didn't invest much time in New Hampshire while putting his post-Iowa focus on South Carolina.

Several of Romney's rivals have made clear they will seek to undercut the chief rationale of his candidacy: that his experience in private business makes him the strongest Republican to take on President Barack Obama on the economy in the fall. Perry, for one, is accusing Romney of "vulture capitalism" that led to job losses in economically distressed South Carolina.

Obama's team, treating Romney as their likely general election opponent, has joined in the effort to darken the picture of his days in private enterprise. Vice President Joe Biden said Tuesday night that Romney had worried more about investors doing well than he did about the employees of companies bought by his venture capital firm.

On Wednesday, Romney offered a practical-minded defense of layoffs that might not reassure voters worried about holding onto their jobs.

"Every time we had a reduction in employment it was designed to try and make the business more successful and, ultimately, to grow it," Romney told ABC's "Good Morning America."

He got some support from an unusual source - his rival Paul, who finished second in New Hampshire. The libertarian-leaning congressman said other Republican candidates were slamming Romney for market-oriented restructuring of corporations.

"I just wonder whether they're totally ignorant of economics or whether they're willing to demagogue just with the hopes of getting a vote or two," Paul told MSNBC on Wednesday.

Romney said his opponents sound like Obama and other Democrats attacking the free enterprise system and encouraging jealousy toward the wealthiest 1 percent of Americans. "It's a very envy-oriented attack," he told NBC's "Today" show.

Romney contends the criticism actually works to his benefit by highlighting the business acumen that will help him set the nation's economy right and shrink the federal government.

TV ads are filling the South Carolina airwaves, including negative spots like a new one from Gingrich assailing Romney for switching his position on an issue that resonates strongly with evangelicals who make up the base of the GOP here.

"He governed pro-abortion," the Gingrich ad says. "Massachusetts moderate Mitt Romney: He can't be trusted."

About $3.5 million already has been spent on TV ads in South Carolina, the bulk of it by Perry and a supportive super PAC. But that doesn't count the $3.4 million a pro-Gingrich group has pledged to spend to go after Romney, or the $2.3 million a pro-Romney group plans to spend in the coming days. Santorum and a super PAC friendly to him also are pouring money into the state, as is an outside group working on Huntsman's behalf.

Expect a flood of more hard-hitting commercials - primarily aimed at the front-runner - in a state known for brass-knuckled Republican politics.

For all of Romney's challenges, the presence of a cluster of socially conservative candidates fighting to be his chief alternative could work in his favor by splitting the vote on the party's right flank. Santorum, Gingrich, Perry and others split the faith-focused vote in Iowa. South Carolina also has a large contingent of evangelical voters, some of whom remain suspicious of Romney.

"I don't know if we can win South Carolina," Romney said Wednesday on ABC's "Good Morning America." He added, "I know it's an uphill battle."

South Carolina could end up being the last stop for some candidates. Perry, for one, has had back-to-back dismal showings and is looking to South Carolina to right his struggling campaign.

"They kind of start separating the wheat from the chaff, if you will," Perry told a cafe crowd Tuesday. "But South Carolina picks presidents."

Gingrich, the former Georgia lawmaker, is also playing on his regional ties, saying, "The ideal South Carolina fight would be a Georgia conservative versus a Massachusetts moderate."

Santorum and Huntsman also have vowed to press on. Santorum wants to claim the conservative mantle; Huntsman eschews ideological labels and is selling himself as someone who can heal a polarized nation.

"Third place is a ticket to ride, ladies and gentleman," Huntsman boomed from the lectern after finishing third in New Hampshire. "Hello, South Carolina."

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Associated Press writers Shannon McCaffrey and Beth Fouhy in New Hampshire and Connie Cass in Washington contributed to this report.

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