Before the assassination attempt on Rep. Gabrielle Giffords in early 2011, it had been quite some time since there had been a major assassination attempt on American soil. The attempt on President Reagan had been almost thirty years earlier. During the intervening time, the naive view that American politics had outgrown such barbaric acts of political violence could grow and thrive. Then in July 2011, the world witnessed an anti-Muslim European go on a shooting spree in a delusional sense of being at war. In his mind, there was an actual war and his acts were justified. In fact, he viewed himself after the fact as a savior. Undoubtedly, there was no internal check in his mind for how far his sense of political reality could get from the “facts on the ground.”
The full essay is at "Bad Psychology and Political Violence."