Josh Marshall says it brilliantly. Excerpt:
I'm under no illusion that negative or even nasty campaigning will come to an end in the USA. I don't think that's realistic or even necessarily desirable. Hard-fought and brass-knuckle politics is something built into the fiber of American politics. It's part and parcel of the intensity of belief and passion that many of us have for the issues at stake in our elections.
But McCain's campaign has devolved into something altogether different ... what with its increasingly open appeals to racial conflict and aggressive invocations of blood hatred of Arabs and Muslims. As The New Republic phrases it, McCain's "subtle incitements of racial warfare and underhanded implications of foreign nativity." Over the months we've become desensitized to the moral depravity of McCain's campaign.
Moral depravity. As good an explanation of the McCain campaign as any I've seen.