I know plenty of smart people that do absolutely fucking retarded things, though.
Who knows how smart he is. But perception is 4/5ths of reality and to anybody with an IQ over about 85 (read: anyone not from the South) Bush is perceived as a fucking looney toon.
Unfortunately, he is very well insulated and comfortable and can basically get away with whatever the hell he wants over the next 11 months or so.