Mitt Romney was unruffled in the New Hampshire Republican debate Saturday night that saw heated exchanges between Ron Paul and his rivals but relatively little criticism leveled against the frontrunner.Rick Santorum, who is riding high after his number two finish in the Iowa caucus, was one of the few candidates to go aggressively after the former Massachusetts governor, taking on his economic plan and health care record.The former senator, who has portrayed Romney as a cold, calculating, chief executive and not an inspirational leader, continued that line of attack tonight.”Business experience doesn’t necessarily match up with being the commander-in-chief of this country,” Santorum said at the debate in Manchester, N.H., sponsored by ABC News, Yahoo! News and WMUR. “The commander-in-chief of this country isn’t a CEO.”Romney responded with a veiled jab at the former senator, saying, “I think people who spend their life in Washington don’t understand what happens out in the real economy.”"The people in the private sector,” Romney continued, “They’re not successful because they’re managers. They’re successful primarily because they are leaders.”Later in the debate, Santorum attacked Romney’s use of the word “middle class,” suggesting that it only adds to President Obama’s and Democrats’ line of argument.”As far as substance, I agree with Speaker [Newt] Gingrich. I don’t think Governor Romney’s plan is particularly bold, or is particularly focused on where the problems are in this country,” Santorum said.Saying that “there are no classes in America,” Santorum took issue with Romney’s use of the word middle class.”We are a country that don’t allow for titles. We don’t put people in classes. There may be middle income people, but the idea that somehow or another we’re going to buy into the class warfare arguments of Barack Obama is something that should not be part of the Republican lexicon. That’s their job, divide, separate, put one group against another,” he said.”I’ll use the language of bringing people together,” he added.Gingrich, who has seen his ranking in the polls slide rapidly, was asked about Romney’s record at Bain Capital but largely left criticism in a scathing TV ad by a super PAC aligned with his campaign to speak for itself. The pro-Gingrich super PAC Winning Our Future recently teased a forthcoming film it produced — called “King of Bain” – that featured interviews with laid off employees, hammering Romney for turning their lives upside down. The video calls Romney’s tenure at Bain “a story of greed.”Gingrich said he hasn’t seen the ad but that “people should look at the film and decide.”"I’m not nearly as enamored of a Wall Street model where you can flip companies, you can go in and have leveraged buyouts, you can basically take out all the money, leaving behind the workers,” he said, taking a swipe at Romney without saying his name.Romney defended his record at Bain, including the fact that some of the companies it invested in led to layoffs. “We understand that in the free economy, in the private sector, that sometimes investments don’t work and you’re not successful,” he said. “It always pains you if you have to be in a situation of downsizing a business in order to try and make it more successful, turn it around and try and grow it again.”View ABC News’ live blog from the debate here.Romney may be the frontrunner but it was Rep. Ron Paul who was the subject of the testiest exchanges of the night. Paul went aggressively at his rivals, accusing Santorum of corruption and Gingrich of ducking military service.Paul and Santorum are engaged in a tooth-and-nail battle for the number two position and the two have had the feistiest exchanges of the debate.”To say you’re a conservative, I think, is a stretch. But you’ve convinced a lot of people of it, so somebody has to point out your record,” Paul charged, citing a report by the Citizens for Responsibility and Ethics in 2006 that named Santorum one of three “most corrupt” senators.Paul’s charge comes at a time when Santorum is trying to make the case that he is the one true, viable conservative alternative to Romney.Santorum bashed CREW as a liberal organization and defended his conservative record.”If you haven’t been sued by CREW, you are not a conservative,” he responded. “It’s a ridiculous charge and you should know better than to cite George Soros-like organizations.”He painted Paul as being far out of the mainstream of the Republican Party: “You vote against everything.”Soon after, Gingrich and Paul clashed in a heated exchange on the question of military service.”I think people who don’t serve when they could and get three or four or even five deferments have no right to send our kids off to war and be even against the wars we have. I’m trying to stop the wars but at least I went when they called me up,” he said.But Gingrich, who received a draft deferment during the Vietnam war on the basis that he had children and was studying, pushed back heavily at Paul’s not-so-veiled jab.”Dr. Paul has a long history of saying things that are inaccurate and false. The fact is I never asked for a deferment. I was married with a child. It was never a question,” he countered. “I personally resent the kind of comments and aspersions he routinely makes without accurate information and then just slurs people.”"When I was drafted I was married with two kids and I went,” Paul responded, to applause.”I wasn’t eligible for the draft. I wasn’t eligible for the draft,” Gingrich repeated.On the issue of foreign policy and how they would handle Iraq and Afghanistan, the candidates deviated little from their talking points, except Rick Perry, who said for the first time that he would send troops back to Iraq. Perry was the only other candidate on stage, besides Paul, to serve in the armed forces.”I would send troops back into Iraq,” he said. “The idea that we allow the Iranians to come back into Iraq and take over that country, with all of the treasure, both in blood and money that we have spent in Iraq, because this president wants to kowtow to his liberal leftist base and move out those men and women. … I think it is a huge error for us.”The Texas governor has long criticized Obama for announcing a date for the troop withdrawal but has previously only said that he would consult with commanders on the ground before making troop decisions.On Iraq, Perry stood out from the rest of the candidates, namely Paul who advocates bringing all troops back home, even from Afghanistan.