Not surprisingly, there has been a lot of research on terrorist attacks within the United States. It turns out that, contrary to the propaganda you are likely to see on television, terrorist attacks by right-wing Christian extremists are at least as prevalent as terrorist attacks by Islamic extremists. The implication of this is that if our country is serious about fighting terrorism on US soil, our counter-terrorism efforts need to be directed toward both kinds of terrorism. Furthermore, the motives, ways and means are different between the two, meaning that a one-size-fits-all approach is bound to fail.
Here’s an article on a recent study: Terrorism In America.