Once again, the overriding lesson, as settled as social science can ever be, remains: If we had gun laws like the gun laws of most countries that resemble ours, we would have lower levels of gun violence, as they do. That would not mean that we would have no gun violence. It means that we would have less gun violence. Deranged fans would not casually assassinate young singers, and young men would not be sending desperate texts to their heartbroken mothers. It is possible to believe both that Islamist terrorism is real and that Islamist terrorism is uniquely empowered here because of the availability of guns designed to kill many people very quickly. It is impossible to make gun terrorism impossible. But it is easy to make gun terrorism hard. It begins with controlling the weapons that terror loves.