Though I don't...

...normally go in for the "Bush is dumb" thing (not because I don't think he is dumb, but because it absolves him of responsibility for all the dumb things he does), this article in Slate at least takes the thought and fleshes it out a bit:

George W. Bush has governed, for the most part, the way any airhead might, undermining the fiscal condition of the nation, squandering the goodwill of the world after Sept. 11, and allowing huge problems (global warming, entitlement spending, AIDS) to metastasize toward catastrophe through a combination of ideology, incomprehension, and indifference. If Bush isn't exactly the moron he sounds, his synaptic misfirings offer a plausible proxy for the idiocy of his presidency.

Go.