His rival Republican presidential candidates slammed Mitt Romney on Monday night in an increasingly desperate effort to stop his momentum toward possible victory in Saturday's South Carolina primary - and with it a likely unshakable grip on the party's presidential nomination.
They took turns in a fiery debate portraying him as a cold corporate titan who cast aside workers to pocket millions and a secretive millionaire whose record would eventually lead Republicans to regret choosing him.
Standing at center stage, the former governor of Massachusetts appeared to brush aside most of the barbs, answering some with a cool detachment, ignoring others, smiling throughout.
Responding to one demand that he release his tax records, the man worth an estimated $250 million said for the first time that he might do that - in April, tax season, after clinching the nomination.
"I'm not opposed to doing that," he said.
The 16th debate of the GOP campaign featured just five candidates for the first time - hours after former Gov. Jon Huntsman dropped out of the race with a warning that the party is obscuring its conservative message with wave after wave of attack ads in Iowa, New Hampshire and now South Carolina.
"This race has degenerated into an onslaught of negative and personal attacks not worthy of the American people," Huntsman said. "At its core, the Republican Party is a party of ideas, but the current toxic forum of our political discourse does not help our cause."
Former rivals ignored his warning.
U.S. Rep. Ron Paul of Texas defended one of his ads blasting former U.S. Sen. Rick Santorum of Pennsylvania as a big spender of taxpayer money.
"If you're exposing a voting record, I think it's quite proper," Paul said of his ad. "I only had one problem. I couldn't get in all the things I wanted to say."
The other candidates - former House Speaker Newt Gingrich, Gov. Rick Perry of Texas and Santorum - used their turns in the spotlight not just to rip Romney but to elbow one another. Each is seeking to emerge as the sole anti-Romney, hoping to rally conservatives.
Gingrich, who once accused the media of trying to stir disagreement among the candidates, defended his attacks on Romney's record as critical to informing voters to avoid "buyers' remorse" after the nomination is wrapped up.
He singled out Romney's role as a co-founder of the Bain Capital private equity investment firm. Too often, Gingrich said, the company left firms "with enormous debt" and forced them to "go broke."
Perry criticized Bain's role in closing a local steel mill in Georgetown, saying Romney's firm "swept in, they picked that company over and people lost jobs."
Romney strived to turn the criticism around, saying he had a record of making tough calls in business, in state government and in saving the 2002 Winter Olympics in Utah. He blamed the steel mill loss on unfair competition from China, and said that helped give him the experience to fight unfair trade.
"I'm the guy who can best post up against Barack Obama," he said.
Santorum lodged some of the sharpest attacks, swinging back at pro-Romney ads saying that Santorum backed allowing felons who have served their time to vote.
Santorum asked Romney his view - a particularly apt question, Santorum said, since Monday was the Rev. Martin Luther King Jr.'s birthday, and "this is a huge deal in the African-American community."
Romney tried to explain that he can't control the ads of independent groups, but Santorum insisted that he answer directly. After some back and forth, Romney said that he did not think that people who have committed violent crimes should regain their right to vote.
Santorum struck back, saying that when Romney was governor of Massachusetts from 2003 to 2007, convicted felons did have that right, even when on parole or probation.
Santorum's aggression put Romney on the defensive. Romney said the Massachusetts state legislature was 85 percent Democratic, and he implied that he saw no way to change that law.
Paul faulted Santorum for voting for the No Child Left Behind education act and for opposing a bill favoring the anti-union right to work.
Santorum replied, "I'm a strong conservative, but I'm not perfect."
He said he was wrong in voting for the education act and that his state, Pennsylvania, opposed right-to-work laws, so he felt obliged to stand by his state on that.
Romney is leading polls in South Carolina by an average of 7.7 percentage points. A win here by the former Massachusetts governor would all but seal his nomination.
Romney eked out an eight-vote victory in the Jan. 3 Iowa caucuses, and won the New Hampshire primary a week later.