No less worrisome, the major nuclear powers (and some smaller ones) are all in the process of acquiring new nuclear arms, which could, in theory, push that threshold lower still. These include a variety of cruise missiles and other delivery systems capable of being used in “limited” nuclear wars — atomic conflicts that, in theory at least, could be confined to just a single country or one area of the world (say, Eastern Europe) and so might be even easier for decision-makers to initiate. The next president will have to decide whether the U.S. should actually produce weapons of this type and also what measures should be taken in response to similar decisions by Washington’s likely adversaries.