Democrats and the Obama campaign have seized upon Mitt Romney’s performance during the Las Vegas debate to intensify attacks on the GOP front-runner as an insensitive, unprincipled and self-serving politician.

“Mitt Romney proved again last night that he will say or stand for anything to get elected, even if it means forgetting the positions he’s previously taken,” Obama campaign manager Jim Messina told reporters on a conference call that focused exclusively on the former Massachusetts governor.

During the 13-minute call, Romney was mentioned by name 16 times, while Texas Gov. Rick Perry and businessman Herman Cain were only each mentioned briefly and in response to reporters’ questions.

Messina took particular aim at Romney’s reaction to an allegation raised during the debate by Perry that Romney had paid illegal immigrants to work on his property.  Romney said he fired the lawn service when he learned of the workers’ status.

“He didn’t object to having undocumented workers working for him because it was illegal. He objected because he thought it would hurt his political career,” Messina said. “His actual quote was, ‘I’m running for office, for Pete’s sake. I can’t have illegals.’”

The Democratic National Committee also pounced on Romney’s line, featuring it in a Web video called “Did Mitt forget?”  (Earlier in the debate, Romney said, “I don’t think I’ve ever hired an illegal in my life.”)

“The core principal that drives Mitt Romney is getting elected,” Messina said. “That is why Romney doesn’t have any credibility when he’s out there saying he’s fighting for the middle class.”

Democrats have been hammering on Romney for weeks on his opposition to a proposed payroll tax cut extension that they say would most benefit middle-class families, Democrats’ health care law and a mortgage modification program sponsored by the Obama administration meant to help struggling homeowners avoid foreclosure.  They say Romney is a political opportunist who is out of touch with the middle class.

“Instead of allowing responsible homeowners to refinance their homes like the president has, Mitt Romney would leave them on their own,” Obama campaign spokesman Ben LaBolt said, citing Romney’s comments this week to the Las Vegas Review-Journal that he would not “try to stop the foreclosure process. Let it run its course and hit the bottom.”

Chief Obama campaign strategist David Axelrod said on CBS’ “Early Show” today, “I think there is a sense there is no core to him.”

The Romney campaign has dismissed the attacks as partisan hits meant to distract from Obama’s economic record. Aides also say the focus on Romney indicates how threatened Obama strategists is by his candidacy, and a sign Romney has emerged as the clear front-runner.

As for the illegal immigration spat, senior Romney adviser Eric Fehrnstrom told reporters after the debate, “Mitt Romney hired a legitimate company, the company in turn hired illegal immigrants. When it was pointed out to Mitt Romney, he told the company to correct the problem. When the company failed to correct the problem, he fired them.”