As Newt Gingrich surges, Mitt Romney is attempting to kneecap the former House speaker, dispatching his top surrogates to slam Gingrich as an egotist and an “untrustworthy conservative.”

In a conference call with Beltway reporters on Thursday morning, former New Hampshire governor John Sununu and former Missouri senator Jim Talent blasted Gingrich’s record, from his “self-aggrandizement” as speaker to his recent criticism of Rep. Paul Ryan’s Medicare plan.

“The off-the-cuff [remarks] that Gingrich throws out on occasion [are] a reflection of the off-the-cuff thinking that he goes through to deal with issues, and that is not what you want in a commander-in-chief,” said Sununu, a former White House chief of staff in the George H.W. Bush administration. Gingrich, he added, has consistently displayed “irrational behavior.”

Talent, who served with Gingrich in Congress, concurred. “Speaker Gingrich was an unreliable leader,” he said. “You were in a situation where you would get up in the morning, and you would have to check the newspaper, the clippings — that was before the Internet — to see what the speaker had said that day, and what you were going to have to clean up.”

The comments from Sununu and Talent highlight the Romney campaign’s latest strategy, confronting Gingrich about his entire record, both in Congress and elsewhere. Publicly, Romney himself is remaining above the fray, focusing on extensive business and managerial experience. In campaign videos, Romney adopts a positive tone, touting his years in the private sector and his longtime marriage to his wife, Ann.

But behind the scenes, it’s a different story. Romney advisers are prepping for a potentially long, brutal battle for the nomination, and today’s remarks were the opening salvo. “This is the time in a campaign where issues will be contrasted between the candidates and I suspect you’re going to hear more than just contrasting styles; you’re going to hear contrasting positions on issues, particularly entitlement reform,” Sununu said, hinting at the coming barrage.

“This is entirely predictable,” says Mike Dennehy, a New Hampshire–based GOP strategist who managed Sen. John McCain’s successful Granite State primary campaigns. “Quite frankly, it’s what Mitt Romney needs to do to try and stop Gingrich’s momentum. He can’t go any further without contrasting with Gingrich. This is standard-operating procedure: carting out one of your big endorsements in the state and seeing what kind of damage they can wage.”

A memo sent to Romney supporters on Capitol Hill underscored this maneuver, detailing the “talking points” the campaign hopes its boosters will use, such as “Gingrich creates theories; Mitt creates jobs,” “Newt Gingrich has run for office 14 times; Mitt Romney spent his career in the private sector,” and “it’s Newt Gingrich who is the social engineer.”

On the call, Talent pointed out that the campaign’s attacks are not meant to be personal, and resisted the opportunity to make personal attacks. Rather, he said, the criticism is part of Romney’s electability argument. “He’ll beat Barack Obama by the biggest possible margin,” he said.

Indeed, the campaign is gleeful about the amount of baggage in Gingrich’s record, with one adviser describing it as a “very long all-you-can-eat buffet.” In coming days, Romney’s team will mount further Gingrich challenges, refreshing Republicans’ memories of Nineties turbulence, with Gingrich’s entire record “fair game.”

“You have these two guys out there, both have white hair, both look somewhat alike, saying the Nineties were great, that they ended welfare, balanced budgets,” the adviser says of Gingrich and Bill Clinton. He notes that voters must pick one of two scenarios: “I’m willing to believe that Bill Clinton was a great president and did all these things. Or, I’m willing to believe what I thought Republicans believed, like what Charles Krauthammer said, that it was a holiday from history,” full of tax increases and defense cuts.

Sources close to the Gingrich campaign tell NRO that campaign aides are more than happy to respond to specific statements, but do not expect Gingrich himself to diverge from his positive persona, which they credit as an integral part of his resurgence in the race.

Speaking in Greenville, S.C., Gingrich reiterated that message, telling reporters that his campaign will “stay positive,” according to Politico. “We’re going to stay solution-oriented and talk about what America needs to do,” he said. “The only opponent I have is Barack Obama.”

Still, as Gingrich smiles amid the potshots, his team is hustling to ensure that GOP voters do not accept the Romney team’s argument. In a private meeting on Wednesday in an Arlington hotel, Gingrich spoke for two hours with longtime conservative-movement activists.

According to two people who attended the meeting, Gingrich did much to shore up his support. “That kind of forum means more to conservatives than whatever Romney people are saying today,” says one attendee. “At least he is meeting with conservatives, taking tough questions. And because he did that, he got a standing ovation.” Another attendee mostly agreed with that assessment, calling the talk “at times uncomfortable for Gingrich, but ultimately a success.”

Richard Viguerie, the longtime conservative fundraiser who helped organize the meeting, tells NRO that movement activists will probably not embrace Romney’s attacks, and points to Sununu and Talent as examples of Romney’s core problem. “Sununu doesn’t know conservatives, and conservatives don’t know him,” he says. “Same with Talent. Neither carries weight nor influence within the movement. They’re good men, establishment Republicans, but to say these two men can speak about Gingrich’s conservative credibility is laughable. It’s just not serious.”

Romney, however, is not the only Gingrich competitor who is challenging the former speaker. Rep. Ron Paul of Texas, who placed second in the latest Des Moines Register poll, is also blasting Gingrich, dubbing him a “serial hypocrite” in a hard-hitting spot that is currently on the Iowa airwaves. A Super PAC supportive of Romney’s campaign is also upping its Iowa ad buys, though, unlike Paul, the pro-Romney ads do not mention Gingrich.

Craig Robinson, editor of TheIowaRepublican.com and a former political director of the Iowa GOP, says the December tangles, including the forceful statements from Sununu and Talent, could shake up the race. Iowans, he says, are shifting from being “really high on Newt” last week to realizing this week that, “geez, there’s a lot of stuff in his background that disturbs us.”

But Romney, Robinson cautions, should be careful about how he attacks Gingrich’s record. “Romney needs to double down on his strengths,” he says, referring to economic issues, “instead of trying once again to appeal to social conservatives, which I just don’t think are going to drift his way no matter what.”

Gingrich advisers, for their part, are shrugging off the blitz, noting that as the clear leader in national polls, they expect attacks. “There is no doubt that these comments reek of desperation,” says former Pennsylvania congressman Bob Walker, a Gingrich adviser. “Romney, who usually has a cool demeanor, is totally changing direction. I’m not sure it’s going to go over well.”

— Robert Costa and Katrina Trinko are NRO reporters.