Obama campaign manager: Romney 'has no credibility' on middle-class issues

President Obama's campaign manager continued to focus on GOP presidential front-runner Mitt Romney on Wednesday, blasting the former Massachusetts governor for having "no credibility" on middle-class issues.

Jim Messina, Obama's top campaign official, said on a conference call that the "core principle that drives Mitt Romney [is] getting elected."

The day after Romney and the rest of the Republican field, most notably Texas Gov. Rick Perry, exchanged harsh and heated words at the GOP debate in Las Vegas, the Obama campaign sought to capitalize on Romney's rough night.

Messina and campaign spokesman Ben LaBolt blasted Romney on immigration, the economy and home foreclosures.

Seizing on comments Romney made in Las Vegas that home foreclosures should run their course, Messina charged that "Romney would leave them on their own."

"Romney doesn't have any credibility when he says he's out there fighting for the middle class," Messina said.

The campaign also hammered a refrain that Romney's "core principle" was getting elected, playing into a theme the Democratic National Committee has built over the past two weeks with their "WhichMitt" online campaign.

Messina seized on a moment in Tuesday's Republican debate when Romney defended himself from charges of his gardening company employing illegal immigrants.

"We went to the company and we said, look, you can't have any illegals working on our property," Romney said. "I'm running for office, for Pete's sake, I can't have illegals."

Messina noted that the governor "didn't object to [employing] undocumented workers because he thought it was wrong," but rather because he was "running for office."

Asked later in the call if the campaign had comments on any other Republicans in the field, Messina and LaBolt declined an invitation, underscoring how seriously the White House was taking their push against Romney.

"It's certainly not up to us to judge the Republican race," Messina said.