Sorry folks, bad move, bad, bad move.
I think that it all depends on the spin. IF (and this is a big IF) McCain can get his message out fast enough, and loud enough, and be perceived as taking the "High Road", then he just sealed the election.
However, if Obama is allowed to grab the focus...McCain just fumbled the ball inside his own 20. It won't break him, but he'll lose whatever small edge he has right now.