German nuclear physicist Carl Friedrich von Weizsäcker said of nuclear weapons, "...mankind now comes into the position that either we will overcome the institution of war, or we will destroy ourselves."
Source: WITNESS, BBC World Service, 2016-May-06, 08:50.
But neither thing has happened yet. The USA has had nuclear weapons since 1945, but hasn't used them in its wars since World War Two. The USA retreated from Vietnam, leaving the country in the hands of its enemy, without resorting to its nuclear arsenal.
If a science fiction story had a side with a powerful weapon refusing to use it, I'd probably say it was ridiculous. But we have seen exactly this in real history.
In fiction there is a dramatic expectation. If you mention the Doomsday Slayey Machine a lot, the Doomsday Slayer Machine has to be part of the story. Either by being used or by a heroic action to stop it firing.
Stephen, what you say is true of the accepted rules of fiction. My point is that in the real world things don't always work the way they're expected to work in fiction.
Trump will be prepared to use the doomsday weapons and hang the consequences