outrage-burnout.
Bush is such a fuck, such a dirty little git, so deserving of everything and anything bad that can possibly happen to him, that it's just hard to get excited over any new bit of crap he spews. His particular evil has become banal. He could decapitate a baby on national TV, spit in its throat, and have sex with the head, and I think a lot of folks would roll over in bed and just mumble "Bound to happen." or "What's new." (Other than the right-wingers who would praise his courageous and self-sacrificing efforts to root out the WMD's that were probably in that babies body.)
After 4 years of his shit, we're just tired.
http://www.theonion.com/