McCain imitates Caligula
Legend has it (according to Seutonius) that the Roman emperor Caligula ordained his horse Incitatus as a priest, and threatened to install that same horse as one of Rome's two consuls (who acted more or less as vice-emperors). Caligula was by all accounts completely insane, but his political promotions of Incitatus served to send a deliberate message: he was telling both the priesthood and the Senate just exactly how little he thought of them by suggesting that his horse was their equal.
By naming Sarah Palin as his running mate, John McCain is imitating Caligula.
The nomination of Palin for the office of vice president sends exactly the same message to the American people and to the US Senate (in which Palin would be the presiding officer and tie-breaking vote): he thinks so little of them that he believes any random fundamentalist wingnut plucked off the street would be qualified to lead them.
Anyone who buys into McCain's message is worse than ill-informed; they're confirming his message.