Actually, McVeigh wasn't acting as a fundamentalist Christian. He was acting in rebellion to the Clinton White House (in general) and the Bureau of Alcohol, Tobacco and Firearms (in the particular).

You can't call Branch Davidians Christians. Christians believe Christ was God incarnate come to die for man's sins. Branch Davidians believe whomever their current leader is (such as David Koresh) also fits that role (except for the he has to die part). Branch Davidians are heretical Christians, if they're Christian at all (and I'd say they're not, and the Nicean Creed is on my side). I can call myself an elderly lesbian waterpolo player, but that doesn't mean I am.