The Republican challengers to Mitt Romney descended on South Carolina on Wednesday sharply divided and deeply uncertain about how to stop the front-runner’s march to the GOP presidential nomination.

Former House speaker Newt Gingrich (Ga.) led the attacks with a tough ad that began airing Wednesday detailing Romney’s past support for abortion rights. After Romney’s victory in New Hampshire on Tuesday, attention turned to South Carolina, which will hold its primary on Jan. 21.

Texas Gov. Rick Perry joined in the assault, picking up the new favorite line of attack against Romney — that the former Massachusetts governor and former private-equity executive bankrupted companies and laid off workers as a management consultant at Bain Capital.

“Venture capitalism is good,” Perry said to about 150 people at Shealy’s Bar-B-Que in Leesville. “But vulture capitalism, I’ve got no use for.”

Gingrich has sent conflicting messages as to how sharply he intends to target Romney. Throughout a negative ad blitz aimed at him in Iowa by a pro-Romney PAC, Gingrich pledged to stick with a positive message. But his tone changed in recent days, and on Tuesday, his spokesman, R.C. Hammond, signaled that South Carolina would be nastier: “The goal is to get rid of Romney. Our goal is to remove Mitt Romney from the competitive ranks.”

But one thing was clear by the end of Wednesday: Even the candidates determined to attack Romney on Bain were having trouble doing that without contradicting their own conservative ideology about the role of market capitalism and prompting a backlash from within their party.

Former Utah governor Jon Huntsman, the third-place finisher in New Hampshire, implored Republicans to drop the Bain issue.

“I think it’s more instructive to look at governor Romney’s record as governor,” Huntsman told reporters after an appearance at the University of South Carolina in Columbia. “You can’t be on both sides of this issue. If you’re going to stand for breaking up the banks, then you can’t criticize Bain Capital for doing some of what it did.”

Other GOP leaders, nervous about the damage such a debate could do to Romney, as well as the entire party, said attacking free enterprise gives President Obama a talking point for the general election.

The tea-party-friendly group Americans for Prosperity assailed the “populist-tinged attacks on free enterprise.”

Romney, after boarding a plane to South Carolina, considered the prospect of a blistering campaign there over the next week and a half and said he did not expect the Bain attacks from his own party.

“We’ve understood for a long time that the Obama people would come after free enterprise,” he said. “I’m a little surprised to see Newt Gingrich as the first witness to the prosecution. But I don’t think that’s going to hurt my purpose. Frankly, if I can’t take a few shots coming from my colleagues on the Republican side, I’m not ready for Barack Obama.”

Gingrich seemed unsure about how to proceed. He steered clear of the issue in his first appearance Wednesday, at the Laurel Creek Club in Rock Hill, where he got a five-minute standing ovation as he strolled onstage.

“It’s good to be home,” said the former House speaker, invoking his ties to neighboring Georgia.

Later in the day, he resumed his sharper tone, railing against “crony capitalism” and demanding that Romney be transparent about his Bain days. Gingrich’s campaign also released a video of “top Romney gaffes.”

Additionally, a pro-Gingrich super PAC posted a half-hour movie about Romney’s days at Bain and announced that $3.4 million in ads with excerpts from that film would begin airing across South Carolina on Thursday.

But when one person asked Gingrich to stop the Bain attacks, he seemed to acknowledge the damage they could cause. “I agree with you,” he said. “It’s an impossible theme to talk about with Obama in the background.”

Gingrich, Perry and former senator Rick Santorum (Pa.) have trained their sights on South Carolina as the final chance for conservative voters who hope to halt Romney, whose victories in Iowa and New Hampshire have made him the man to beat.

Santorum declined to join in the Bain attacks on Romney: “I have chosen a different course,” he said as he signed autographs after a Wednesday evening town hall meeting in Columbia. “I believe in capitalism, and I believe that unfortunately some businesses fail. I can’t imagine too many businesses invest in a company so they would fail.”

During his speech, Santorum questioned the assertion that Romney is the most electable candidate. “When has he ever proven that?” he asked.

At a packed rally in Columbia late in the day, Romney appeared with South Carolina Gov. Nikki Haley, and even his rivals concede that if Romney wins here, stopping him will be nearly impossible.

Nonetheless, South Carolina, with large numbers of evangelicals and social conservatives, is not especially fertile ground for Romney, and his opponents know they are running out of options.

Gingrich’s spokesman, Hammond, issued a statement saying: “Romney’s record as CEO of Bain is fair game and it will be vetted in the view of the public.”

Even Huntsman, who warned against Bain attacks, sent mixed signals. His spokesman, Michael Levoff, walked back his candidate's remarks late in the day: “Governor Huntsman believes Romney has an electability problem regarding his time at Bain, but he does not believe attacking the venture capital business model is productive.”

Bob Walker, a close friend and longtime ally of Gingrich’s who served with him in the House, said Wednesday that he had called Gingrich to talk about the South Carolina campaign. While he didn’t directly criticize the attacks on Romney or Bain, he said he thinks the message should be focused on Obama.

Other Republicans simply watched with trepidation.

“Newt can get angry about things, and I think he’s frustrated,” said Cindy Costa, a Republican national committeewoman from South Carolina. “He was on such a high at one point it looked like he was going to be the shoo-in for the nomination, and then it all just went kind of downhill. But I think he’s been in politics long enough to know that it would not benefit anyone to have a scorched-earth strategy.”

Others believe that the intensity of the battle will strengthen the eventual nominee.

“You hear this every time,” said South Carolina GOP Chairman Chad Connelly. “ ‘Primaries are a bloodbath.’ ‘Primaries are a bare-knuckled fistfight.’ I think it’s part of the vetting process, the thick-skin-toughening process that’s part of the primary.”

Whatever happens, South Carolina is widely viewed as the firewall. The state has chosen the eventual Republican nominee in every primary since 1980.

Staff writers Steve Hendrix, Sandhya Somashekhar and Rachel Weiner contributed to this report.