Nuclear war may at times seem the stuff of a bygone era. But with Iran and North Korea growing their nuclear weapons programs, a rapid acceleration in China, and a flagging U.S. arsenal—nuclear weapons are back on policymakers’ radars. Here, Brad Roberts, director of the Center for Global Security Research at Lawrence Livermore National Laboratory and an affiliated researcher at IGCC, analyzes the challenges ahead for the Biden administration—both to contain growing threats and modernize the U.S. enterprise.