What word or phrase describes a person who invests in an enterprise that he knows is a scam or Ponzi scheme? Can the word or phrase refer to a person who votes for a politician who repeatedly tells known lies?
I'm tempted to suggest sucker - a person who is easily tricked or deceived. But if a person knowingly does something stupid, then is he or she being tricked?
But if I'm just splitting hairs, then sucker might be a good choice.
As deadrat suggest, some people such as you describe could be called Republicans, but many others could be called Democrats, including the astonishingly clueless Obamabots.
In the political arena, the term sheeple pretty well covers conservatives and liberals alike.
Words like idiot, airhead and dimwit might work, but sucker has a connotation of being sucked in to a scam.