Peter Bergen and David Sterman at CNN write:

...since 9/11 extremists affiliated with a variety of far-right wing ideologies, including white supremacists, anti-abortion extremists and anti-government militants, have killed more people in the United States than have extremists motivated by al Qaeda's ideology. According to a count by the New America Foundation, right wing extremists have killed 34 people in the United States for political reasons since 9/11. (The total includes the latest shootings in Kansas, which are being classified as a hate crime).

By contrast, terrorists motivated by al Qaeda's ideology have killed 21 people in the United States since 9/11.

I don't know about you, but when I'm on a plane and a white guy with short hair gets on, I start to get nervous. Shouldn't they be screening people like that or something?