Other responses seem strange in darker ways. One of the strangest is the idea, recently endorsed by Betsy DeVos, the secretary of education, that putting guns in schools will reduce school shootings. After the Pittsburgh synagogue shooting, President Trump seconded the motion: “If they had some kind of protection inside the temple, maybe it could have been a very much different situation.”

I think of the crowded school library in which my son died. I try to imagine a librarian drawing her Glock and returning fire.

This scenario resonates for me. A few years ago, tired of being told by gun rights people that I knew nothing about firearms, I bought a handgun and learned to carry and use it. I found the transgressive nature of the exercise stimulating. Survivors of gun violence are not supposed to walk around with guns. I also discovered, to my surprise, that shooting was therapeutic. I was mastering the instrument of my suffering. Now I reckon I’m at just the level of casual knowledge that a gun-owning janitor or history teacher might be expected to have attained. What if I’d been in that library in 1992, charged with keeping my son safe?

I put the question to a man I know, a retired Alcohol, Tobacco and Firearms agent who specializes in training people to use guns defensively — the kind of training that this administration might want to give teachers, the kind that the National Rifle Association imagines could stop the killer in a mass shooting.

This man spoke with me about the low proficiency of the average gun owner: “Imagine shooting hoops in your driveway and thinking you can play in the N.B.A.” He spoke of the hundreds of hours necessary to achieve the Zen-like level of expertise in which, in the midst of chaos, responses are instantaneous and instinctive. He spoke of the continual training necessary to maintain those skills, and he generously agreed to take me through an abbreviated version of that curriculum, training intended to turn an average shooter into, well, what exactly? I wasn’t sure.