So if you haven't heard about the "birthers" movement, there is a fringe portion of the Republican party which argues that Obama is not an American citizen so therefore he is a criminal and can't be president. Here' s a funny video of Replication representatives literally running from a Huffington Post reporter instead of answering questions about whether they think Obama should be President or not.
The term "birthers" seems to have come from the 9/11 conspiracy theorists, who were called "truthers". Here's the Birthers page on Wikipedia. Pretty scary stuff. What is amusing is that it is a poison pill for the Right. They can't disagree with their vocal base but they can't agree because it will marginalize them.