Where Ross Douthat sees a double standard, I see the effect of racism:

Well, unless the abuse of the race card actually exacerbates racial tensions, by constantly framing the ordinary rough-and-tumble of political combat as Jim Crow come again. It is, of course, possible that the North Carolina GOP was trying to stoke fears of miscegenation by running the (strikingly unsexual, to my admittedly-Yankee eye) photo of Perdue with Obama, just as it’s possible that the famous anti-Harold Ford ad from last year was trying to send out a “Harold Ford is going to rape your daughters, white America” vibe with its inclusion of a blonde, bare-shouldered bimbo from the Playboy party telling Ford to call her. But in both cases, it’s worth noting that the ad in question could have been cut exactly the same way if the candidate it attacked were white. If Obama were a white politician being criticized for his ties to a left-wing white preacher (yes, they do exist), the difference between the two photos of the N.C. politicians would be chalked up to Obama having appeared with Perdue and not with Moore - if, that is, anyone stopped to ponder the difference at all. Likewise, if Ford had been a white Democrat with a reputation as a dandy and a ladies man running a populist and religion-infused campaign in a Southern state, the “call me, Harold” ad would have been treated as the clever culture-war foray it was, and either celebrated or criticized on those grounds.

The basic fact is that the ubiquity of racist attitudes makes this kind of “what if” near-impossible.  As one of Ross’ commenter’s noted, if Obama (or Ford) weren’t black, then there is a good chance that this ad would have never been made.  Implying a white man’s promiscuity with white women just isn’t the same as showing a black man with a white woman.  The former would probably just bring out a voter’s inner moral scold, but there’s a better than good chance that the latter would generate a primal sort of racial fear, which is far more powerful than simple disapproval.

Whether it is fair or not, it’s simply the case that when certain (largely routine) accusations are thrown at a black politician, they take on a racial tinge.  Calling a white politician corrupt is par for the course, but calling a black politician corrupt - especially in the South - conjures up Reconstruction-era “fear of a black planet” anxieties.  Now, assuming that most people in the national media understand this point (and there is some evidence that they do), this has a definite benefit for the Obama campaign.  There’s a good chance that - whenever a racially-tinged ad is aired - the media will latch on to it and repudiate it as a racially-tinged ad.  And if the existing research is still valid (Tali Mendelburg’s The Race Card is a great place to start), then by repudiating the racial message of an ad, the media will have neutralized its effectiveness (since implicit racial priming is only effective when voters aren’t cognizant of it).