THOMAS BEAUMONT Associated Press ROCK HILL, S.C. (AP) - Attacked as a corporate raider, Mitt Romney defended his record in a new television ad Friday that accuses Republican presidential rivals who criticized his time at the helm of a private equity firm of "embarrassing themselves by taking the Obama line."

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At the same time, Romney's allies were assailing rival and former Sen. Rick Santorum in ads in South Carolina and Florida for pork-barrel spending as they worked to keep the challenger, who has avoided criticizing Romney's business past, from catching fire while Romney pushes for a four-state win streak.

"Mitt Romney helped create and ran a company that invested in struggling businesses, grew new ones and rebuilt old ones, creating thousands of jobs," says Romney's new ad in South Carolina that lists Staples, Sports Authority and Steel Dynamics as successes of the Bain Capital venture firm.

"We expected the Obama administration to put free markets on trial ... Romney's GOP opponents are embarrassing themselves by taking the Obama line."

That line was a slap at Newt Gingrich and Rick Perry, who have gone after Romney over his Bain tenure and drawn criticism from across the GOP for doing so.

As if on cue, Obama's campaign released a scathing memo noting that Bain closed companies and cut wages and benefits, while Romney and his partners became wealthy.

The memo amounts to a roadmap of the Obama campaign's general election playbook should Romney become the GOP nominee.

"His overwrought response to questions about it has been to insist that any criticism of his business record is an assault on free enterprise itself," top Obama campaign aide Stephanie Cutter wrote. "But this is just an attempt to evade legitimate scrutiny of the record on which he says he's running."

Romney also rolled out a radio ad about values in South Carolina - likely to counter a TV ad by Gingrich that hits Romney on abortion - and one in Nevada promoting his jobs experience.

Romney and his allies are the only presidential campaign entities on the air in Florida, running moderate to heavy levels of ads.

With the Bain issue now spreading across both the primary and general election campaigns, Romney was looking to blunt the force of attacks on the central rationale for his candidacy in hopes of preventing those criticisms from taking hold, if they haven't already. It's unclear whether attacks by Gingrich and his allies are having an impact on the race in South Carolina, where unemployment is high.