As the early primaries draw near, Newt Gingrich’s Achilles’ heel could be the millions he was paid by Freddie Mac.

Yesterday morning, top rival Mitt Romney called on Gingrich to return the money during a Fox News appearance. For Gingrich, Romney’s request was merely the latest in series of blows since Bloomberg first reported the payments, estimated at $1.6–$1.8 million, in mid-November.

“It’s a perfect argument against Gingrich because it ties him to the sleazy practices of the beltway when he is trying to run as an outsider,” observes Larry Sabato, director of the Center for Politics at the University of Virginia.

During Saturday night’s debate, Ron Paul hammered Gingrich on the issue, saying that Gingrich had “received a lot of money from Freddie Mac.”

“Freddie Mac [was] bailed out by the taxpayers,” Paul continued. “So in a way, Newt, I think you probably got some of our taxpayers’ money.”

Paul isn’t simply spreading that meme in debates. He’s also pushing the message in two attack videos his campaign has released online — both of which have scored links on the Drudge Report. The two versions of the first video — one is ad-length, the other longer — have together been viewed over 1 million times. On an appearance on Meet the Press on Sunday, Paul commented that he wouldn’t “have taken their money just for the fact that I think it’s an immoral thing.”

Bachmann, too, has harshly criticized Gingrich for “shilling” for Freddie Mac. “Whether former speaker Gingrich made $300,000 or whether he made $2 million, the point is that he took money to influence senior Republicans to be favorable toward Fannie and Freddie,” Bachmann said in November.

“Speaker Gingrich has been part of the Washington excesses and crony capitalism that Governor Huntsman wants to eliminate,” e-mailed Huntsman spokesman Tim Miller. Neither Rick Perry’s campaign nor Rick Santorum’s responded to a request for comment on whether their candidates agreed that Gingrich should return the money.

Sabato is dubious that the Freddie Mac association will harm Gingrich unless several of the candidates pick up the theme and run with it. “It might work if it becomes a standard refrain among the other candidates,” he says. “Let’s face it: It is sleazy. Plus, the explanation:‘I was a historian, I wasn’t a lobbyist’? There’s no one who buys that.”

Right now, in early-primary states, the on-the-ground sense is that Freddie Mac charges aren’t influencing how voters view Gingrich. “The Freddie Mac profits have thus far not had an impact on Newt Gingrich,” says Tim Albrecht, communications director for Iowa governor Terry Branstad. “Since the news came out, he has continued to rise in the polls. I think the complexity of the issue makes it difficult to explain and makes it a difficult punch to land.”

Veteran New Hampshire strategist Mike Dennehy is similarly skeptical, saying that it “depends on how the issue is characterized and framed.”

“I think it basically goes in one ear — and a voter says ‘Wow, that’s a lot of money, he’s making a lot of money’ — and then it goes out the other ear,” Dennehy observes. “It’s a sophisticated issue. So, most voters aren’t going to be able to connect the dots between his consulting fee and the scandal surrounding Freddie Mac.”

But while voters may be unmoved by Gingrich’s Freddie connection, campaigns could use it as a way to highlight Gingrich’s seeming tendency “to contain multitudes,” as it were. After all, Gingrich hasn’t been quiet about those who allowed the Freddie Mac and Fannie Mae scandal to happen. In an October debate, he insinuated that former Democratic senator Chris Dodd and Democratic congressman Barney Frank should go to jail for their role in the debacle.

As for Gingrich’s rivals, the Freddie Mac reminders could serve yet another purpose: getting Gingrich to lose his cool.

The ex-speaker, who had pledged last week to stay “positive” on the campaign trail, wasted little time in responding to Romney’s request that he return the Freddie Mac money.

“If Governor Romney would like to give back all the money he’s earned from bankrupting companies and laying off employees over his years at Bain, then I would be glad to then listen to him,” Gingrich told reporters. “And I will bet you $10, not $10,000, that he won’t take the offer.”

— Katrina Trinko is an NRO reporter.