Nuclear terrorism is the greatest national security threat facing the United States. This is a point on which few disagree, yet the effort to reduce the global nuclear threat falls short in terms of speed, resources, and level of effort. This article presents four hypothetical nuclear crises to illustrate this point and suggests a series of steps that, if taken, could help prevent each crisis. We are in a race between cooperation and catastrophe, and the global threat is outpacing our response. We must act now.