I think breaking his "No New Taxes," pledge is what doom Bush.

Not surprising, left leaners trend towards more taxation so "no new taxes" is a bit of an insult to them. A slight leftward lean is all that differentiates Democrats from Republicans and the "independents" are about as equally divided ideologically as their partisan counterparts.

If the failure to uphold a promise of "no new taxes" was a trigger issue among right leaning independents then they would be pissed off enough to come out in slightly higher numbers against the failing executive.
Good coffee, good weed, and time on my hands...