Came across this post on polling on the question of whether or not the respondent believes Obama was born in the US. While there was an initial dip after release of the long form birth certificate, numbers are back to where they were before hand. The partisan divide remains just as strong.
Currently, 55% of Americans believe Obama was born in the US while 20% state this is false, the remainder respond not sure. Among Republicans, 31% believe Obama was born in the US while 33% state this is false. I have trouble believing those are truly honest statements, but then again I have encountered the odd birther who feels the need to bring it up even when basically irrelevant to the conversation; there may be a larger minority that believes this privately that doesn't wear the belief on their sleeve.
This is simply one more piece of data showing how hard it is to change beliefs with data as well as how much stronger group think and tribalism are than individual level rationality. I think this is an important point to drive home, too often we talk about social, political, and economic issues as if they can be analyzed through a framework of individual level rationality despite an overwhelming amount of evidence that resistance to data and individual level rational thinking not only exists, but is rather common.
(h/t Monkey Cage)