Why?

I've been trying to figure out why smear sticks only to Democrats, even when the smear on the Democrats is false and the smear on Republicans is true. Take Palin/McCain. (Please, take them away.) They are lying repeatedly about all kinds of things, among them the "bridge to nowhere," Obama's earmarks, Palin's misuse of authority to punish her sister's ex, etc., etc. The press, for a change, have actually reported on this stuff pretty thoroughly and yet McCain/Palin continue to lie about these things. It's as if they're sticking their middle finger in the air and saying, "F#*k you. If I want to tell a lie, I'll tell a lie. Let's see what you'll do about it." And, the public says, "that's just politics." But, when Obama says McCain is trying to put lipstick on a pig by calling himself a change agent, and McCain howls about how nasty a slur this is to Palin, the public outcry against Obama is deafening. I don't think it's just the press coverage. Of course, some of it is the well-organized Republican noise machine. The Democrats haven't even come close to matching that -- to their endless shame. But, I'm not even sure that explains it fully. There's some sort of IOKIYAR (it's okay if you're a Rebuplican") thing going on here with the public. They're much more inclined to overlook nastiness if it comes from Republicans and to blame Democrats as nasty even when they're not. But why? That's what I haven't figured out.