Not so long ago, it was implausible that a major nuclear power — the United States, Russia, or China — would consider using atomic weapons in any imaginable conflict scenario. No longer. Worse yet, this is likely to be our reality for years to come, which means that the next president will face a world in which a nuclear decision-making point might arrive far sooner than anyone would have thought possible just a year or two ago — with potentially catastrophic consequences for us all.