WASHINGTON — Donald J. Trump’s remarks on nuclear weapons have brought him, at times, to a question: Why should he be constrained from ever using them?
The question has, like so many of Mr. Trump’s comments, sent shock waves. But nuclear experts say it is shocking not just for the statements themselves, but for the uncomfortable truths they expose, perhaps unwittingly, about nuclear weapons.
President Dwight D. Eisenhower, though at first a proponent of using nuclear weapons, eventually deemed them too destructive to consider. “You just can’t have this kind of war,” he said in 1957. “There aren’t enough bulldozers to scrape the bodies off the streets.”
Yet the United States and other nuclear powers have maintained and expanded their arsenals, enhancing their ability to launch nuclear strikes even as they have concluded that the logic of such a conflict makes using the weapons unthinkable.
This idea became known as mutually assured destruction, in which countries wield nuclear weapons primarily to deter other nuclear powers. But this deterrent works only if it is credible.
This leads to an odd dynamic: The more willing leaders are to use nuclear weapons, the less likely they will need to do so. Leaders heighten the risk — making the weapons faster, more powerful and harder to stop — so as to minimize it. They make the weapons more usable precisely because they are not.
There is little in Mr. Trump’s comments to suggest that he intended to highlight this contradiction, but that is what he did in asking why the United States bothers to develop extravagantly expensive weapons it never intends to set off.