Twice every year, the FBI assembles the National Mission Force for Marble Challenge, a complex inter-agency test of the ability of the blackest parts of the federal government to find and “render safe” a ticking nuclear bomb. It is the domestic counterpart exercise to Vital Archer I wrote about yesterday that takes place in Canada, and a drill that has become more and more sophisticated over the years, folding in not just conventional and unconventional military assets but also scientists from the Department of Energy, the Environmental Protection Agency, and the Centers for Disease Control and Prevention.

In the dark, they come in, shielded from public view by a police perimeter and an inner line of uniformed guardians. The target is reserved for the Tier I forces: They’ve practiced hundreds of times, rappelling onto the roof, banging down doors, hop-scotching down corridors, sweeping rooms. When it’s all clear, the scientists are ushered in with their detection gear and their “render safe” machines and tools. The orders are crystal clear: Do everything and anything to get to the nuke before it explodes, take no chances, shoot to kill.