The waters of Katrina continue to transform the American political landscape, separating, among other things, conservatives from rascists. Though the notion that Republicans are coming over "to the left" is a bit far-fetched, there are considerable numbers of Republicans who are genuinely horrified by what they saw. (David Brooks is perhaps the best example.) They aren't likely to rethink their whole world view (though some may), instead they are slowly and inevitably beginning to write-off Bush as an incompetent. (Very reminiscent of the way that many Russian monarchists gave up on Nicholas II before 1917.)
Bush has only two real loyal constituencies in this crisis--cronies and rascists. That's his rock solid "base". Let's not kid ourselves, there are a lot of rascists all over the country but for Bush Co. or the Republican Party this is not a winning formula.
The big political problem for Bush Co. is that his performance in this crisis is having a multiplier effect. It is giving serious weight and substance to Republican doubts about his competence in other matters and particularly his management of the war Iraq. If the war is far away, people can put it out of their minds. Katrina, however, was an up close and personal look at Bush "in action". What ultimately sealed Bush's fate, I think, were eight simple words, "Brownie, you're doing a heck of a job".
The meme of "Bush incompetence" has taken firm hold and, at this point, there is little that Bush Co. can do to change that image. And for the Republican Party, this poses real problems for the long-term future. Among other things, the "culture of life" issue--the bedrock of Republican culture wars--is in the process of being completely redefined. How many people drowned in nursing homes because help did not arrive in the days after Katrina? (This is the image that FEMA is desperately trying to censor).
Bush is finished, spent as a political force. The question is whether the Democrats will be able to change the national conversation.