I think Joe Klein has this right. McCain's "gaffe" today--saying that we're down to pre-surge levels in Iraq when we aren't--strikes me as careless and not very revealing of anything. But you can hardly fault the Obama campaign for pouncing. The GOP, after all, spent a good part of the week gratuitously attacking Obama's trivial misstatement of which Nazi concentration camp his uncle's army unit liberated in World War II.
Both Obama and McCain say they want to run high-minded, civilized campaigns that rise above the pettiness of Washington politics. So far I don't see much sign of that. And the problem is, once you get into "he-started-it!" territory, it's awfully hard to go back.