Judging from his Internet postings, Jared Lee Loughner is a delusional young man whose inner political landscape is a swamp of dystopian novels, left- and right-wing tracts, conspiracy theories, and contempt for his fellow human beings. He refers to the gold and silver standard; that doesn't make Ron Paul responsible for the shootings. He is fond of “Animal Farm”; George Orwell didn't guide the hand that pulled the automatic pistol's trigger. Marx and Hitler produced a lot of corpses, but not the ones in Tucson.

But the plate-glass window of Congresswoman Gabrielle Giffords’s office was shattered last March after the final health-care vote. Judge John Roll, who was among the dead, had received death threats and spent a month with a protection detail. Roll was apparently a bystander to Loughner’s intended target—and maybe the gunman had no idea why he was aiming for Giffords either, maybe he didn't know how she voted on health care or what her position on Arizona’s draconian immigration law was. It would be a kind of relief if Loughner operated not out of any coherent political context but just his own fevered brain.

But even so, the tragedy wouldn't change this basic fact: for the past two years, many conservative leaders, activists, and media figures have made a habit of trying to delegitimize their political opponents. Not just arguing against their opponents, but doing everything possible to turn them into enemies of the country and cast them out beyond the pale. Instead of “soft on defense,” one routinely hears the words “treason” and “traitor.” The President isn't a big-government liberal—he's a socialist who wants to impose tyranny. He's also, according to a minority of Republicans, including elected officials, an impostor. Even the reading of the Constitution on the first day of the 112th Congress was conceived as an assault on the legitimacy of the Democratic Administration and Congress.

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 TV 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.

Photograph: Mamta Popat/Arizona Daily Star/AP