I've written often in the past about appeals to tribalism, and the "He's not one of us" argument is something that 1) you almost always hear from Republicans, not Democrats, and 2) you hear much more often in the South than anywhere else. You're much more likely to see an ad saying that a candidate has "South Carolina values" or "Oklahoma values" than one saying a candidate has "Oregon values" or "New York values." Perhaps that will change as people from places dominated by liberals get a more clearly defined tribal identity linked to their geography, but in the past it's been the South where the lines between "us" and "them" are clearest. It's not necessarily racial in the strict sense that whites are part of "us" and blacks are part of "them," but race is almost always implicated. Someone who's a little too Northern in their history or their sympathies is part of "them" in part because they're too solicitous of the interests of blacks.
All that notwithstanding, identity is a complex thing that can be wielded in the service of any ideology. To wit:
That's right, it's a Barack Obama ad that ends with these words on the screen: "Mitt Romney. Not one of us." Not too much subtlety there.
So, should this be condemned? I'll admit my biases and grant that perhaps I'm more inclined to give Obama a pass than I would if the ad was by a Republican. But there is a reason why this may be more a venal sin than a mortal one. The key question is, who is the "us" we're talking about? In this case, Obama is trying to convince voters that Romney is alien from them not because of the color of his skin or his religion, but because of what he did at Bain Capital. "Us" is defined in this case by class and power, and as much as conservatives whine about "class warfare," there isn't too much to be worried about if the rich are targets of resentment. What with not only the comforts of their lives but the fact that the political system, the economic system, the education system, and pretty every other system is shaped by them for their benefit, they can tolerate a little criticism.
And frankly, the tag line on the ad is so blunt it wouldn't surprise me if the Obama campaign was hoping for a little controversy that would give them some free airtime and push forward a discussion of just how bad Romney's business behavior was. We'll see if anyone takes the bait.