A variety of nuclear weapons are needed for deterrence to ensure adversaries know the U.S. can employ proportional responses to nuclear attacks, the head of the National Nuclear Security Administration said today. "Maybe you don’t want to escalate,” Administrator Brandon Williams said at the Hudson Institute. “Maybe if you are trying to reestablish deterrence after they’ve crossed the threshold, you want something that signals to your adversary that you are just as serious. And again, it’s not tit for tat,...