The catastrophic danger posed to cities by nuclear weapons is nothing new. Putting major urban areas at risk across generations is, in fact, the point of these weapons of terror. The practice of doing so is benignly called nuclear deterrence, but it requires holding the cities of adversaries – real and imagined – under constant threat. The use of even the smallest nuclear weapons in today’s arsenals would cause a humanitarian emergency in cities. That is why city leadership should have a voice...