John McCain's presidential campaign is threatening a lawsuit against the National Enquirer over a print edition story the tabloid ran today alleging that Gov. Sarah Palin has had an extramarital affair with her husband's business partner. The allegation would normally be dismissed by political observers as the random musings of a supermarket tabloid -- indeed, the McCain campaign said as much in its statements on Wednesday -- except that the paper has built up a reservoir of legitimacy following its earlier reporting on the John Edwards affair. In a statement to the Huffington Post, a spokesman for the paper, who promised a larger report next week, tapped into that pool of quasi-respect. "The National Enquirer's coverage of a vicious war within Sarah Palin's extended family includes several newsworthy revelations, including the resulting incredible charge of an affair plus details of family strife when the Governor's daughter revealed her pregnancy. Following our John Edwards' exclusives, our political reporting has obviously proven to be more detail-oriented than the McCain campaign's vetting process. Despite the McCain camp's attempts to control press coverage they find unfavorable, The Enquirer will continue to pursue news on both sides of the political spectrum." Clearly, this is a touchy matter. Already, rumors that Palin's youngest son was actually the son of her daughter were batted down. And the McCain campaign has strenuously insisted that the current crop of insinuations is not only false but also potentially libelous. "The smearing of the Palin family must end. The allegations contained on the cover of the National Enquirer insinuating that Gov. Palin had an extramarital affair are categorically false. It is a vicious lie," said McCain senior adviser Steve Schmidt. "The efforts of the media and tabloids to destroy this fine and accomplished public servant are a disgrace. The American people will reject it." But the Edwards reporting complicates matters. Just one month ago, conservatives were bemoaning the fact that no major media outlets had the temerity to follow the politically and personally sensitive rumors about the former North Carolina senator's infidelities. Jonah Goldberg, for example, wrote on the National Review's the Corner in later July that: "Whatever the merits of the whole Edwards love child story, are we really supposed to believe that one of America's most famous trial lawyers wouldn't sue a publication that printed defamatory and slanderous lies about him? Also, it's worth pointing out that while the Enquirer may or may not be scrupulous in its choice of stories -- that's in the eye of the beholder -- it is pretty scrupulous about its facts. They win lawsuits. They've broken a host of stories the MSM guys couldn't." Does the MSM now have an obligation to pursue this rumor, however touchy, or at least ask questions? "The "success" with Edwards no doubt will give them some more credibility, although we should remember that some of the allegations in their "lovechild" stories have been far from proven (although also far from disproven)," wrote Greg Mitchell, editor of Editor and Publisher Magazine. "Some of their Palin revelations may be quickly firmed up, prove bogus or more likely rest somewhere in-between for awhile. But what will be interesting is whether the Republicans and conservatives and MSM critics who jumped on the MSM and liberals for not quickly embracing the Enquirer's Edwards work will now pooh-pooh the Enquirer when it comes to THIS candidate....:" And yet, at the same time, the Enquirer's story may be something of a break for the McCain campaign, which has come under siege for the Palin pick. If the Arizona Senator and his aides are able to effectively portray attacks on the Palin as the product of smear, sleaze and innuendo, it clouds those that are more legitimate. And with new attack lines opening up against Palin seemingly every hour, Democrats may be even more hesitant about straying into the tawdry.