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 2008 campaign. 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.