Posted 11 Aug 2017.
The answers provided by others are very interesting, however many have not cast light upon one individual in the whole decision-making process who has (from my perspective) a bit more “pull” than is typically considered: the Secretary of Defense, James Mattis.
A quick Google search shows that Mattis is very much a realist when it comes to the idea of employing nuclear weapons against North Korea. For good reason: aside from the international reactions, the guaranteed refugee/humanitarian disaster that will immediately follow poses enough of a threat to the nations in close proximity to North Korea – as well as the responsibilities that the US would inherit as a result of such action – complicate any considerations in the use of force.
If the President issues such a strike, it will be interesting to see what resistance he will get from Mattis. I have no doubt that the Secretary of Defense will comply, if it comes to that, but the conversations and advice given on the matter will be scrutinized for decades.
provided a very detailed answer to the question While I am not an expert in the field of Mutually Assured Destruction (MAD) and the steps to properly descend into such… um… madness, the steps he provided mirror everything I have found on the topic…