Bush = Nazi Religious Nut
Kerry = Pussified Communist
Those are the darkest comic book fears swing voters have about the two men. (of course one is more accurate than the other) During the home-stretch each man will have to act against type to reassure voters on the fence, so over the next 68 days Bush needs to be more sensitive and sane while Kerry needs to act more like Jesus H. Hitler.
In a race that starts tied I'll take the guy who actually helps his image by being brutal and one dimensional. Every Bush attack is an opportunity for Kerry to be a real prick, and passing the "real prick" test is an honest-to-god threshold in American Presidential politics. (related article:
http://www.nypress.com/print.cfm?content_id=10369)
By demolishing all possible standards of campaign decency Bush has now empowered Kerry to cut loose at a time that Bush will not be able to respond without looking CRAZY.
Analogy: An old-style duel where one man fires and misses and then has to stand there while the other guy aims at leisure.