I've been hanging around the United Nations these past few days attending events related to consultations on lethal autonomous weapons systems—so-called killer robots. These are AI-powered weapons systems that can select and strike targets without human control. This is not the stuff of science fiction. These weapons exist today, and they are becoming more powerful—and, frankly, more accessible. They can be relatively inexpensive and deployed by both states and non-state actors, including terrorist groups.