Before the United States Marine Corps allowed me to carry a live M-16 assault rifle, I went through hundreds of hours of firearms training. Classroom sessions devoted to nomenclature, maintenance and basic operation accounted for more than two weeks of study before I even set eyes on ammunition. For weeks, I carried an M-16 without a magazine — a dummy weapon, basically. I secured it with a padlock overnight while I slept in the barracks, and unlocked it each morning before chow.

Only at the shooting range was I allowed to check out magazines and ammo from the armory. The first day at the range I spent 12 hours disassembling, cleaning and reassembling the weapon. I had to do this blindfolded. I had to do this while a drill instructor hurried me, yelling that enemies were at the gate. I had to do this while fellow Marines wept nearby from doing hundreds of burpees as punishment for not being able to reassemble their weapons fast enough.

The military issue M-16 is the model for the AR-15 assault rifle that the accused shooter used to kill 17 people this month at Marjory Stoneman Douglas High School in Parkland, Fla. The shooter bought the weapon lawfully. He received zero hours of mandated training. There is no reason that any civilian, of any age, should possess this rifle.

At the White House on Wednesday, President Trump suggested that if a football coach at the high school, Aaron Feis, had been armed, he would have saved even more lives than he did, perhaps even his own, because rather than simply shielding students from gunfire, he could have drawn his weapon, fired and killed the assailant — putting a tidy end to the rampage.