Romney steps up defense of business record Mitt Romney greets supporters at a campaign rally in Columbia, South Carolina, on Wednesday. Mitt Romney defends his record at Bain Capital Pro-Gingrich group promises to spend $3.4 million in South Carolina ads attacking Romney South Carolina GOP Sen. Jim DeMint criticizes the attacks on Romney's business record South Carolina's January 21 primary is widely seen as a critical contest (CNN) -- GOP presidential frontrunner Mitt Romney aggressively defended his tenure as head of Bain Capital Thursday, once again asserting that his private equity career resulted in the net creation of over 100,000 jobs while also calling any job losses an unfortunate fact of life in the private sector. "The reality is in the private sector that there are some businesses that are growing and thriving, and we were fortunate enough to be able to be a part of that in a small way," Romney told reporters after a campaign event in South Carolina. But "there are some businesses that have to be cut back in order to survive. ... Sometimes we're successful at that, and sometimes we're not. Romney said any job loss is a "tragedy," but insisted that every time Bain "invested in a business it was to try and encourage that business to have ongoing life." Fresh off a solid win in Tuesday's New Hampshire primary, Romney is now aiming for what many analysts believe would be a knockout blow in South Carolina's January 21 contest. The conservative Palmetto State has picked the winner of every GOP nomination fight since 1980. Several of Romney's rivals -- most notably former House Speaker Newt Gingrich and Texas Gov. Rick Perry -- are furiously trying to prevent a Romney win by hammering the former Massachusetts governor on his private sector track record. Perry recently castigated Romney for practicing "vulture capitalism" that generated wealth for a select few while gutting companies. An outside group backing Gingrich has promised to spend $3.4 million in South Carolina television ads largely blasting Romney's business record. Strategists for the group -- Winning Our Future -- believe the ads will have particular resonance in a state with a reeling manufacturing sector and unemployment hovering close to 10%. GOP critics of the ads have characterized them as a form of class warfare better suited for a Democratic than a Republican campaign. South Carolina Sen. Jim DeMint, a GOP powerbroker who has declined to endorse any of the candidate so far, defended Romney's record during an interview with MSNBC Thursday morning, and called the focus on Bain a "teachable moment." He also minimized Perry's and Gingrich's chances in the race, and said that "to damage a frontrunner makes no sense to me." Three prominent DeMint loyalists -- including a former top fundraiser for Perry -- are planning to publicly endorse Romney Thursday, a source confirmed to CNN. One of the loyalists, former South Carolina GOP Chairman Barry Wynn, told CNN the escalating rhetoric about Romney's business background is "destructive." "It's just a dance I didn't want to be a part of," Wynn said. It kind of falls into this politics of envy that the Obama campaign is going to be all about between now and November. Meanwhile, the pro-Romney group Restore Our Future announced the release of a new television ad Thursday ripping Gingrich's record. The ad, titled "Desperate," says the former speaker "has more baggage than the airlines." It focuses on Gingrich's past ties to mortgage giant Freddie Mac and his previous association with Democratic House leader Nancy Pelosi, among other things. The group indicated it plans to spend $2.3 million airing the ad in South Carolina, along with $3.4 million in Florida, which holds its primary at the end of the month. In addition, a group backing Rick Santorum is planning to buy $600,000 in new South Carolina ad time, a source familiar with the buy confirmed to CNN Thursday. The Red, White, and Blue Fund has already purchased $190,000 in ads touting Santorum's conservative principles. Santorum's campaign has said it intends to spend at least $1.5 million in the state. "I challenge you," Santorum told voters Thursday morning at a Palmetto State rally in Bluffton. You have a very important role to play, a huge role to play. If South Carolina gets it wrong, this country may be stuck with four more years of Barack Obama. ... We will be the generation that will have to explain to your children and grandchildren as to what you did, the opportunity you missed. Without naming Romney, Santorum said Wednesday that electing a moderate would be little better than having a Democratic president. "That's not a victory at all," Santorum said, adding: "We want a leader that believes in us and is not an establishment candidate who's going to do more of the same." Gingrich told a town hall Wednesday in Rock Hill, South Carolina, on Wednesday that the result of the state's upcoming primary will be historic. "I believe the next 10 days are as important as any 10 days we have seen in modern American politics," Gingrich said. I believe that South Carolinians are either going to center in and pick one conservative or by default they are going to send a moderate on to the nomination. CNN currently estimates that Mitt Romney has won 25 GOP national convention delegates, compared to 10 for Texas Rep. Ron Paul, eight for Santorum, four for Perry, three for Gingrich, and two for former Utah Gov. Jon Huntsman. 1,144 delegates are needed to win the Republican nomination. Santorum, who lost the Iowa caucuses to Romney by eight votes, said Wednesday it's "silly" for anyone to suggest the former Massachusetts governor has the nomination wrapped up. "This is a long process," he insisted. CNN's Alan Silverleib, Dana Bash, Peter Hamby, Paul Steinhauser, Robert Yoon, and Rachel Streitfeld contributed to this report