Actually, Dubya has already nailed Kerry on this. As soon as Kerry made the statement the first time, The President asked something like this: Maybe Senator Kerry can tell us whether Great Britain was co-erced or was bribed?
Kerry's so far out on a limb right now, staking out his "final position" on Iraq, that all W has to do is shake the tree a bit and Kerry will fall flat on his butt, early in the first debate.
It's going to be W by a knock-out.