I first noticed it during active-shooter situations and terrorist attacks. Everybody would agree that what was happening was horrible, of course, the injuries or even deaths and the destruction. But that wasn’t the part that really seemed to move people. What people really found exciting was arguing about who was probably at fault in the period before that became common knowledge. And the sides were clear: People on the Left would predict that the terror had been wrought by someone on the Right or by a member of the Right’s favored groups, and people on the Right would predict that the terror had been wrought by someone on the Left or by a member of the Left’s favored groups. Once I saw it somewhere, I saw it everywhere. Sometimes the debate persists even after the case had been solved, as in the Pulse nightclub shooting in Orlando in 2016. The shooter, who killed about 50 people, had sworn allegiance to the Islamic State, but because Pulse was a gay club, some commentators worked to classify it primarily as an instance of anti-LGBT violence rather than of Islamic fundamentalist terror. At the extreme, an attack with a clear target might be called a “false flag” — a staged event, one in which people victimize themselves or a group they’re part of to gain some status in the public eye or to bring their favored issues, generally...