How does it work?
We depend on early warning, always have.
We also depend on decisions made by the NCA to assess the threat warnings, determine validity, conference with all NCA and when found to be a valid threat the NCA will bring in the president and his advisors to the conference and the president will be given his options. The president may implement one of the options or do nothing. If an option is selected it is implemented.
This general scenario has been out in the public through various documentaries, books and articles over several decades. The information has been put out there to assure the public over the years that there is no “red button” option.
I spent most of my military career either as a keyturner or as a part of an NCA component. I have never lost a minute of sleep over the idea of an illegal order of this type; even under the Kenyan.