When you heard the terrible news from Arizona, were you completely surprised? Or were you, at some level, expecting something like this atrocity to happen?

Put me in the latter category. I’ve had a sick feeling in the pit of my stomach ever since the final stages of the 2008campaign. I remembered the upsurge in political hatred after Bill Clinton’s election in 1992 — an upsurge that culminated in the Oklahoma City bombing. And you could see, just by watching the crowds at McCain-Palin rallies, that it was ready to happen again. The Department of Homeland Security reached the same conclusion: in April 2009 an internal report warned that right-wing extremism was on the rise, with a growing potential for violence.

Conservatives denounced that report. But there has, in fact, been a rising tide of threats and vandalism aimed at elected officials, including both Judge John Roll, who was killed Saturday, and Representative Gabrielle Giffords. One of these days, someone was bound to take it to the next level. And now someone has.

It’s true that the shooter in Arizona appears to have been mentally troubled. But that doesn’t mean that his act can or should be treated as an isolated event, having nothing to do with the national climate.

Last spring Politico.com reported on a surge in threats against members of Congress, which were already up by 300 percent. A number of the people making those threats had a history of mental illness — but something about the current state of America has been causing far more disturbed people than before to act out their illness by threatening, or actually engaging in, political violence.

And there’s not much question what has changed. As Clarence Dupnik, the sheriff responsible for dealing with the Arizona shootings, put it, it’s “the vitriolic rhetoric that we hear day in and day out from people in the radio business and some people in the TV business.” The vast majority of those who listen to that toxic rhetoric stop short of actual violence, but some, inevitably, cross that line.

It’s important to be clear here about the nature of our sickness. It’s not a general lack of “civility,” the favorite term of pundits who want to wish away fundamental policy disagreements. Politeness may be a virtue, but there’s a big difference between bad manners and calls, explicit or implicit, for violence; insults aren’t the same as incitement.

The point is that there’s room in a democracy for people who ridicule and denounce those who disagree with them; there isn’t any place for eliminationist rhetoric, for suggestions that those on the other side of a debate must be removed from that debate by whatever means necessary.

And it’s the saturation of our political discourse — and especially our airwaves — with eliminationist rhetoric that lies behind the rising tide of violence.

Where’s that toxic rhetoric coming from? Let’s not make a false pretense of balance: it’s coming, overwhelmingly, from the right. It’s hard to imagine a Democratic member of Congress urging constituents to be “armed and dangerous” without being ostracized; but Representative Michele Bachmann, who did just that, is a rising star in the G.O.P.

And there’s a huge contrast in the media. Listen to Rachel Maddow or Keith Olbermann, and you’ll hear a lot of caustic remarks and mockery aimed at Republicans. But you won’t hear jokes about shooting government officials or beheading a journalist at The Washington Post. Listen to Glenn Beck or Bill O’Reilly, and you will.

Of course, the likes of Mr. Beck and Mr. O’Reilly are responding to popular demand. Citizens of other democracies may marvel at the American psyche, at the way efforts by mildly liberal presidents to expand health coverage are met with cries of tyranny and talk of armed resistance. Still, that’s what happens whenever a Democrat occupies the White House, and there’s a market for anyone willing to stoke that anger.

But even if hate is what many want to hear, that doesn’t excuse those who pander to that desire. They should be shunned by all decent people.

Unfortunately, that hasn’t been happening: the purveyors of hate have been treated with respect, even deference, by the G.O.P. establishment. As David Frum, the former Bush speechwriter, has put it, “Republicans originally thought that Fox worked for us and now we’re discovering we work for Fox.”

So will the Arizona massacre make our discourse less toxic? It’s really up to G.O.P. leaders. Will they accept the reality of what’s happening to America, and take a stand against eliminationist rhetoric? Or will they try to dismiss the massacre as the mere act of a deranged individual, and go on as before?

If Arizona promotes some real soul-searching, it could prove a turning point. If it doesn’t, Saturday’s atrocity will be just the beginning.