This relentlessly hostile rhetoric has become standard issue on the right. (On the left it appears in anonymous comment threads, not congressional speeches and national T.V. programs.) And it has gone almost entirely uncriticized by Republican leaders. Partisan media encourages it, while the mainstream media finds it titillating and airs it, often without comment, so that the gradual effect is to desensitize even people to whom the rhetoric is repellent. We’ve all grown so used to it over the past couple of years that it took the shock of an assassination attempt to show us the ugliness to which our politics has sunk.

The massacre in Tucson is, in a sense, irrelevant to the important point. Whatever drove Jared Lee Loughner, America’s political frequencies are full of violent static.