Nuclear nonproliferation was a top priority for the Obama administration. While the Iran Deal was a diplomatic victory toward this end, major threats persist from both state and non-state actors. Countries like North Korea, Russia, and India and Pakistan continue to challenge nonproliferation efforts. The possibility that terrorists will carry out an attack using a "dirty bomb," made from captured nuclear materials, looks increasingly real. In a fractious world, which way forward for U.S. nuclear security policy?