I blame the shitty educational systems as well as our culture. Americans simply don't prize intelligent like other nations do. People who don't believe in Evolution are truly idiots.
If that poll has been done just among of your politicians, the outcome would be different, and believers of evolution would be a small minority. Mechanism behind that phenomena is simple, because all successful experts of mass manipulation has based their skills on religion trough the history of man. To be successful in politics, you have to touch peoples feelings, not their intelligence. If you think about it, you see it your self. God bless the America, god bless the queen, go and fight for home, religion and your country, and if you survive, it is a work of god. If you die, it was meant to be. God bless the fighters on both sides of the front line, god's name may be different, but who the hell can prove who have a right one. If you want to be a politician, you have to have religious mind, little clever perhaps but you never can have real intelligence, that's bad for politicians. Why? You have to be stupid enough to believe that crap which you are feeding to people, if you don't, you lost your credibility. Furthermore, if you put up a survey of IQ among a religious people and supporters of darwinism, you see the fact that religious people score very low average. Politicians vs. stockbrokers from wall street? Politicians lost with a difference of more than 20 points average. Funny part is that they rule your world, they make your laws trusting to god and divine guidance, same as every country you can name.