MYRTLE BEACH, S.C. -- bMitt Romney's four remaining challengers are keeping the spotlight on the Republican front-runner's wealth and business dealings by pressing him to release his income tax returns. Romney says he might make them public in April. By then, he hopes to have the presidential nomination in the bag.His rivals did their best to knock the former Massachusetts governor off stride in a contentious debate Monday night, going after him on several fronts. Romney didn't bend under heavy pressure on the issue of his job-creation record at his former private equity firm Bain Capital, nor did he apologize for his evolving views on abortion. Blamed for negative commercials flooding South Carolina's airwaves, he stressed the independence of the super PACs that have been running ads in his behalf against former House Speaker Newt Gingrich and other rivals, including former Sen. Rick Santorum.
Romney said that while he might be willing to release his tax returns, he wouldn't do so until tax filing time. The multimillionaire former businessman didn't get much gratitude from his rivals, who want him to release the information in time to influence South Carolina voters going to the polls on Saturday.
Gingrich was quick to suggest Romney wouldn't delay for months if he had nothing to hide and that his hesitation wouldn't sit well with voters. "Last night weakened him," Gingrich told "CBS This Morning" on Tuesday.
Romney seemed hesitant when confronted with the tax issue on stage. He at first sidestepped calls from his rivals to release his returns, then said later that he'd follow the lead of previous presidential candidates.
"I have nothing in them that suggests there's any problem and I'm happy to do so," he said. "I sort of feel like we're showing a lot of exposure at this point," he added.
Monday's night's debate was as fiery as any of the more than dozen that preceded it. Romney, the clear front-runner for the GOP nomination after back-to-back wins in the Iowa caucuses and the New Hampshire primary, was under fire not only from Gingrich and Santorum, but also from Rick Perry and Ron Paul.
The five will meet again in debate in Charleston Thursday night, the last time they will share a stage before the primary two days later.
The first Southern primary could prove decisive in the volatile contest. Gingrich has virtually conceded that a victory for Romney in South Carolina would assure his nomination as Democratic President Barack Obama's Republican rival in the fall, and none of the other remaining contenders has challenged that conclusion.
That only elevated the stakes for Monday night's debate, where the attacks on Romney often were couched in anti-Obama rhetoric.
"We need to satisfy the country that whoever we nominate has a record that can stand up to Barack Obama in a very effective way," said Gingrich.
The five men on stage also sought to outdo one another in calling for lower taxes. Texas Rep. Ron Paul won that competition handily, saying he thought the top personal tax rate should be zero.
In South Carolina, a state with a heavy military presence, the tone turned muscular at times.
Gingrich drew strong applause when he said: "Andrew Jackson had a pretty clear idea about America's enemies. Kill them."
Perry also won favor from the crowd when he said the Obama administration had overreacted in its criticism of the Marines who were videotaped urinating on the corpses of Taliban fighters in Afghanistan.
Gingrich and Perry led the assault against Romney's record at Bain Capital, a private equity firm that bought companies and sought to remake them into more competitive enterprises, with uneven results.
"There was a pattern in some companies ... of leaving them with enormous debt and then within a year or two or three having them go broke," Gingrich said. "I think that's something he ought to answer."
Perry referred to a steel mill in Georgetown, S.C. where, he said, "Bain swept in, they picked that company over and a lot of people lost jobs there."
Romney said the steel industry was battered by unfair competition from China. As for other firms, he said, "Four of the companies that we invested in ... ended up today having some 120,000 jobs." And he acknowledged, "Some of the businesses we invested in were not successful and lost jobs."
It was Perry who challenged Romney to release his income tax returns. The Texas governor said he has already done so, and Gingrich has said he will do likewise later in the week.
"Mitt, we need for you to release your income tax so the people of this country can see how you made your money. ... We cannot fire our nominee in September. We need to know now," Perry said.
Later, a debate moderator pressed Romney on releasing his tax returns. His response meandered.
"If that's been the tradition I'm not opposed to doing that," Romney said. "Time will tell. But I anticipate that most likely I'm going to get asked to do that in the April time period and I'll keep that open."
Prodded again, he said, "If I become our nominee ... what's happened in history is people have released them in about April of the coming year, and that's probably what I'd do."
April is long after the South Carolina primary and the Republican nomination could easily be all but decided by then, following Super Tuesday contests around the country in March.
Santorum stayed away from the clash over taxes, instead launching a dispute of his own. He said a campaign group supporting Romney has been attacking him for supporting voter rights for convicted felons, and asked Romney what his position was on the issue.
Romney initially ducked a direct answer, preferring to ask Santorum if the ad was accurate.
He then said he doesn't believe convicted violent felons should have the right to vote, even after serving their terms. Santorum instantly said that as governor of Massachusetts, Romney hadn't made any attempt to change a law that permitted convicted felons to vote while still on parole, a law the former Pennsylvania senator said was more liberal than the one he has been assailed for supporting.
Romney replied that as a Republican governor, he was confronted with a legislature that was heavily Democratic and held a different position.
He also reminded Santorum that candidates have no control over the campaign groups that have played a pivotal role in the race to date.
"It is inaccurate," Santorum said of the ad assailing him. "I would go out and say: `Stop it. That you're representing me and you're representing my campaign. Stop it."'
That issue returned more than an hour later, when Gingrich said he too has faced false attacks from the same group that is criticizing Santorum. He noted that Romney says he lacks sway over the group, "which makes you wonder how much influence he would have if he were president."
Romney said he hoped no group would run inaccurate ads, and he said the organization backing Gingrich was airing a commercial that is so false that "it's probably the biggest hoax since Bigfoot."
He called for scuttling the current system of campaign finance laws to permit individuals to donate as much money as they want to the candidates of their choice.
Noting that the debate was occurring on Martin Luther King Jr. Day, one moderator asked Gingrich if his previous statements about poor children lacking a work ethic were "insulting to all Americans, but particularly to black Americans."
"No," Gingrich said emphatically, adding his aim was to break dependence on government programs. "I'm going to continue to find ways to help poor people learn how to get a job, learn to get a better job and learn someday to own the job," he said.
Romney is the leader in the public opinion polls in South Carolina, although his rivals hope the state's 9.9 percent unemployment rate and the presence of large numbers of socially conservative evangelical voters will allow one of them to slip by him.