It is worth recalling that Bush is estimated at 95th percentile when it comes to intelligence. Not the smartest man in the country by a long shot, but not so far down the totem pole either.

Found this: http://en.wikipedia.org/wiki/U.S._Presidential_IQ_hoax#IQ_estimations_by_academics
I suppose my perception of him was biased, and I'm not even American! Well, time to update...

(It would be interesting to look at the percentiles politicians have in various dimensions- intelligence, height, beauty, verbal ability, wealth, etc.- and see how the distributions differ. This isn't the Olympics, where you're selecting on one specific trait, but an aggregation- and it may be that intelligence does play a large role in that aggregation.)

I recall reading somewhere that somebody bothered to check and it turned out that height and physical looks correlate with political success. Which is not surpising considering the Halo effect.