As a result, the next president will have to grapple with nuclear weapons issues — and possible nuclear crises — in a way unknown since the Cold War era. Above all else, this will require both a cool head and a sufficient command of nuclear matters to navigate competing pressures from allies, the military, politicians, pundits, and the foreign policy establishment without precipitating a nuclear conflagration. On the face of it, that should disqualify Donald Trump. When questioned on nuclear issues in the first debate, he exhibited a striking ignorance of the most basic aspects of nuclear policy. But even Hillary Clinton, for all her experience as secretary of state, is likely to have a hard time grappling with the pressures and dangers that are likely to arise in the years ahead, especially given that her inclination is to toughen U.S. policy toward Russia.