It is facile and mistaken to attribute this particular madman’s act directly to Republicans or Tea Party members. But it is legitimate to hold Republicans and particularly their most virulent supporters in the media responsible for the gale of anger that has produced the vast majority of these threats, setting the nation on edge. Many on the right have exploited the arguments of division, reaping political power by demonizing immigrants, or welfare recipients, or bureaucrats. They seem to have persuaded many Americans that the government is not just misguided, but the enemy of the people.

That whirlwind has touched down most forcefully in Arizona, which Pima County Sheriff Clarence Dupnik described after the shooting as the capital of “the anger, the hatred and the bigotry that goes on in this country.” Anti-immigrant sentiment in the state, firmly opposed by Ms. Giffords, has reached the point where Latino studies programs that advocate ethnic solidarity have actually been made illegal.