MCCAIN’S ‘SECRET ANTI-ROMNEY AD’….With the polls narrowing in New Hampshire, Mitt Romney’s campaign has launched a negative TV ad against John McCain, noting the senator’s votes against Bush’s tax cuts, against a repeal of the estate tax, and for an immigration-reform bill the GOP’s far-right base condemns as “amnesty.” The commercial says McCain is “an honorable man,” but asks, “Is he the right Republican for the future?”

Slate’s John Dickerson obtained a McCain ad — ironically, created by media advisors who quit McCain’s campaign to join with Romney — that Dickerson calls “the perfect counterpunch” to Romney’s latest spot. (Apparently, the McCain campaign put the ad together six months ago, but sat on it, allegedly “reluctant” to go negative.)

The McCain team’s response is that Romney has to talk about the future because he’s spent much of the campaign running from his past. This may become more than a quip if the campaign decides to air the following television ad, which they’ve had on the shelf since the spring.

The ad hangs Romney with his own words — he advocates for a woman’s right to choose and gun control, gets tongue tied on his own hunting practices, and distances himself from Ronald Reagan).

You can see the “secret” ad here, which hits Romney for having been a moderate-to-liberal Republican on culture-war issues. Dickerson sees this as the kind of ad that could seriously undermine Romney’s campaign. I don’t see it that way at all.

Here’s the thing: everyone, including Republican voters, knows all about Romney’s previous beliefs. He’s spent the entire year assuring conservatives, or at least trying to, that he bears no resemblance to his former self. To hear his pitch, Romney is a convert to the conservative cause. (Whether one believes his transformation is sincere or not is another matter entirely.)

McCain, however, has a record that a lot of Republican activists may not remember, and unlike Romney, he hasn’t been peppered with questions about his Republican apostasy throughout 2007. Romney’s ad hits McCain on taxes and immigration, but he also championed sweeping campaign-finance reform with Russ Feingold that conservatives generally hate, joined with John Edwards to support a Patients’ Bill of Rights that conservatives generally hate, voted against an anti-gay constitutional amendment that conservatives generally love, and told a national television audience in 2004 that he would consider joining the Democratic ticket as John Kerry’s running mate.

Indeed, in April 2004, just as the national Republican campaign was beginning in earnest, McCain said, “I believe my party has gone astray…. I think the Democratic Party is a fine party, and I have no problems with it, in their views and their philosophy.”

Everyone knows Romney was pro-choice; does everyone know McCain said this? I kind of doubt it.

Dickerson argues that McCain has the “perfect” response to Romney’s criticism of his record. But unless McCain is prepared to do what Romney has done — disavow everything he used to believe — McCain has far more to lose from this fight.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.