This video hits the nail on the head.
If Obama's name was David O'Donnell, republicans would be behaving differently. Joe Wilson wouldn't have felt free to shout out "you lie!" He felt free to do it, to let his emotions over take him because a black man as president doesn't make sense to him. Joe Wilson, who has this sort of vacant look about him, something in his eyes, may not consciously realize he's a racist. Same with Beck, Limbaugh. They find all of these justifications for what they say and do.
But this is what the tea baggers, the birthers, the tenthers, the deathers....are all about. They're afraid. They're afraid because they perceive Obama as different.
For folks who live in diverse communities, there are all kinds of people and we dabble in other cultures. We are familiar with people who aren't white.
For "white culture" folks, mostly older people, diversity is new and scary. Obama represents something new and scary, especially since many younger people supported him.
Republicans are exploiting this. But more than that, I think they've been emboldened by the fringe. Every week it seems they take another step into Fringeville.