The brilliance of the attack was only apparent after the defensive move was made. McCain has joined Bush to campaign in Nevada and Washington (at Fort Lewis, as close as Bush can get to Seattle without having tomatoes thrown at him). Why campaigning with Bush now? "First time I was asked, " McCain explained.
And there it is! A year ago, Rove & Bush were ridin' confidently along on high polls & war fervour, never for a moment thinking they would need McCain's support. And that shows how smart the Kerry campaign was when they floated the idea of McCain as VP: They increased the media stock of a rival Republican (not to mention one Bush no doubt hates because McCain has the history meritrious conduct Bush lacks), they enticed numerous channels & newspapers to spend airtime and column inches saying "How awesome would Kerry-McCain be?" which is to say, "Wow, wouldn't that be better than Bush-Cheney?" AND that helps paint Bush as being Rightwing in contrast to Kerry-McCain as being Moderate.
A year ago, Rove probably expected Bush to be THE dominant political personality, and Kerry has managed to open a new front on them. Just as Nixon's trip to China made the USSR a little less certain of itself, so have Kerry's overtures to McCain pulled Bush down a little.
I expect to see some more smart moves like these as we get closer to November.