Bush "wins" if he doesn't lose.
The legitimately undecided voters who tune into the debates have in their mind the media's version of Bush - a bumbling idiot who cannot tie his shoe laces with out help.
The expectations are so low that assuming he does not pull a "Ford" and "liberate" Tibet or something, he can't hurt himself.
Also, a lot of people are themselves afraid of public speaking, and seeing a guy a tad awkward is something most people have a baseline sympathy for.
All I know id thatevery time Bush had a big speach, his poll numbers go up a bit.
I don't pretend to understand it, but it seems to be true.
Yeah Kerry is too cerebral and talks too much, and Bush has better advisors at this point, nevertheless Kerry will still probably win the debates.