In my lifetime American children being murdered at school by their fellow students has become an almost unremarkable occurrence.

How did this happen? When Eric Harris and Dylan Klebold killed 12 of their classmates and one teacher in Columbine, Colorado, it was a generation-defining moment, like the assassination of President Kennedy. It was not only the scale of the slaughter that astonished Americans who followed the story in the still early days of 24-hour cable news; it had only been a few years since the bombing of the Alfred P. Murrah Federal Building in Oklahoma City, killed 168 people. But the Oklahoma City bombers Timothy McVeigh and Terry Nichols were terrorist lunatics who looked the part. They were monstrous adults whose victims had included children, circumstances that are not exactly unknown in human history. Harris and Klebold were themselves children — awkward, misfit children with few friends to be sure, but children all the same — killing other children with cold military efficiency.

Columbine frightened everyone. Politicians, educators, parents, those of us who were students ourselves asked how this had been possible. There was a ludicrous but understandable and even touching overreaction in which any hint of violence became the object of outsized concern. I can remember having to speak with the school guidance counselor in fourth grade because my friend and I had a conversation about a character being shot in Star Wars.