A 2007 poll found that Democrats were far more likely than Republicans to say President George W. Bush knew in advance about the 9/11 attacks. A lot of them would believe he has the ExxonMobil logo tattooed on his chest.
The natural human tendency is to accept anything that supports one's existing view and reject anything that doesn't. It beats constantly assessing information to determine whether it's true or false, which is hard, endless, unpaid work.
Yale political scientists John Bullock, Alan Gerber and Gregory Huber say partisans don't just say false things about the opposition; they actually, sincerely believe them. These scholars asked respondents various factual questions about Obama, Reagan and Bill Clinton -- and offered monetary rewards for correct answers. Yet even when money was at stake, partisans still had a clear tendency to give answers (and make errors) that matched their preconceptions.
This is surprising only if you think of political views as a matter of logical reasoning. For many people, they really aren't. They're a way of indulging emotional impulses without suffering painful consequences.
If you insist on believing your fairy godmother will take care of the rent, you'll pay a high price by being evicted. But if you believe equally implausible things about politics, you will pay no price at all.
On the contrary, if thinking Obama is a foreigner brings you closer to people you like, you come out ahead. Birthers would rather be wrong than be divided from their allies. So the fiction that Obama was born in Kenya will endure, and many Americans will hold fast to a ridiculous article of faith that has been conclusively refuted.
It's a thunderous testament to how far people will go in deluding themselves. What's next? Half the country thinking there's at least a chance the moon is made of green cheese?
Don't be silly. No sentient American adult would say that. Unless Obama said it wasn't.