Five things we learned from Monday's debate Rivals finally find a way to rattle front-runner Mitt Romney Gingrich's "food stamp president" quip earns night's biggest applause Bain Capital attacks on Romney resume Strong military presence makes Paul a tough sell in S.C. Myrtle Beach, South Carolina (CNN) -- The five remaining Republican candidates sparred in a Republican presidential debate in South Carolina, five days before that state's primary and three days before a CNN debate in the same state. While front-runner Mitt Romney was again the biggest target on stage, his rivals landed a few punches on each other, too. Romney gets rattled The Republican front-runner hasn't let one of his rivals get under his skin since a CNN debate in Las Vegas in November, when Rick Perry pointed out that Romney once hired a contractor that employed illegal immigrants. Since then, in debates and on the campaign trail, Romney has largely floated above his rivals and trained his fire on Barack Obama instead. But Rick Santorum finally managed to get Romney flustered early in the debate. Santorum said a pro-Romney super PAC was distorting his Senate vote to allow convicted felons to vote after they served out their time in prison. Romney seemed to be caught flat-footed when Santorum pressed Romney to say whether he, too, supported felon voting rights as governor of Massachusetts. Romney was evasive, pausing to gather his thoughts and game out a response. "We have plenty of time; I'll get there," Romney said to Santorum. Romney then took several minutes to answer, finally saying that violent offenders should not be allowed to vote in any circumstance. Santorum pounced, pointing out that Massachusetts felons were, in fact, allowed voting rights during Romney's tenure. Perry joined the pile-on, demanding that Romney release his full tax returns, something he has so far refused to do. Romney dodged that question until later in the debate, when moderators put him on the spot. He again refused to answer directly, saying that he might release his full tax records "around the April time period." "We are showing a lot of exposure at this point," he said, awkwardly defending the financial records he has released so far. The tense exchanges recalled the October 2007 Democratic presidential debate in Philadelphia, when Hillary Clinton's rivals piled on the frontrunner after she would not take a firm position on whether illegal immigrants should be allowed to have driver's licenses. The moment was damaging to Clinton because it reinforced a concern among Democrats that she was a typical politician who would say anything to get elected. Romney has faced the same skepticism from Republican primary voters for almost five years, and Santorum and Perry managed to raise those doubts again Monday. Newt's night Gingrich, dueling with Santorum to win over the anti-Romney conservative vote in South Carolina ahead of Saturday's primary, needed a burst of momentum on Monday. And moderator Juan Williams did him a favor. Williams asked Gingrich about his controversial idea to put children to work as janitors in order to teach them a work ethic. He also pressed Gingrich on whether one of his favorite campaign lines -- that President Barack Obama is "a food stamp president" -- is offensive to minorities. Gingrich seized the moment and played directly to the Republican base, blasting the "liberal" and "politically correct" line of questioning. "First of all, Juan," he lectured, "the fact is that more people have been put on food stamps by Barack Obama that any president of American history." "I believe every American of every background has been endowed by their creator with the right to pursue happiness," he continued, "and if that makes liberals unhappy, I'm going to continue to find ways to help poor people learn how to get a job, learn how to get a better job and learn some day to own the job." The result: The most raucous applause of the night. Bain is back! After dialing back their tough criticisms of Romney's record at the private equity and venture capital firm Bain Capital past in recent days, Gingrich and Perry reprised their attacks during Monday's debate. Their assault on Romney's private sector record has been sharply condemned as an attack on free enterprise by conservative thought leaders and high-profile Republicans like South Carolina Sen. Jim DeMint (who told reporters after the debate that "the Bain stuff is a crock.") But in the debate, Gingrich refused to back down and said questions about Bain are "perfectly legitimate" topics for a political campaign. "The governor has every opportunity to answer those questions, to give us facts and dates, and that's part of his responsibility as a candidate," Gingrich argued. Perry, who has called Romney a "vulture capitalist," pointed to a steel mill in the South Carolina town of Georgetown that went out of business after Bain "swept in" and "picked that company over." Romney responded by pointing to thousands of other jobs that Bain created around the country, and calling job losses an unfortunate reality in a free market system. Will their attacks on Romney's corporate resume resonate in a party that celebrates unbridled free market capitalism? In a state with an unemployment rate approaching 10%, maybe. Interviews with voters across South Carolina over the last week, though, suggest that the Gingrich and Perry strategies are making Republicans uncomfortable. But the Bain genie is now out of the bottle. And Democrats, who are guaranteed to paint Romney as a greedy Gordon Gekko in a general election likely to focus on job creation, are gleeful about it. Maryland Gov. Martin O'Malley, the Democratic Party's chief surrogate at the South Carolina debate, was asked about the Bain criticisms in an interview Monday with CNN. O'Malley's answer? It's always good to have bipartisan agreement. Santorum slashes Newt After saying as recently as Saturday that he largely planned to ignore Gingrich in the final week of the campaign and focus on Romney, Santorum had a change of heart on Monday. Gingrich had spent the day on the stump questioning Santorum's electability, so the former Pennsylvania senator fired back -- and aggressively. During the debate, he challenged the fiscal underpinnings of Gingrich's plan to reform entitlements. And in the spin room, Santorum went even harder at the former House Speaker, calling his entitlement plan "fiscally irresponsible." "He creates a new entitlement and is going to borrow money to do it," he told reporters. He also pushed back against Gingrich's claims that with a split conservative electorate in South Carolina, a vote for Santorum is essentially a vote for Romney. Santorum pointed out that he soundly beat Gingrich in Iowa and "kicked his butt" across New Hampshire. "I am a friend of Newt," Santorum said. He is good man, but the idea of someone who is 0-2 in races to say that I am hurting him? Yeah I am hurting him. I am beating him. The tough new rhetoric from Santorum is a sign that his campaign realizes a kid-gloves strategy toward Gingrich won't help him in South Carolina. Instead, he is now working to undermine Gingrich's credibility among South Carolina conservatives to bring the anti-Romney set into his corner. Paul's problem in South Carolina No one can question his principled stands on the issues, but Ron Paul faces the same conundrum in every debate. When he plays the libertarian card and blasts the "out of control" spending habits of Washington, he scores with the small government conservatives who have energized the GOP since Obama took office in 2009. But his foreign policy views continue to get him into trouble with Republicans. Late in the debate, Paul went on a lengthy rant about "war mongering" and the need to drastically scale back American military activity overseas, views that are largely out of step with most Republican voters. Unlike Iowa and New Hampshire, where Paul fared well in the first two contests of the Republican race, South Carolina has a substantial armed forces presence and several military bases across the state. As a consequence, his foreign policy diatribe was met with an angry chorus of boos from a rowdy audience that was mostly allowed to run wild by debate producers.