The problem with that is Trump isn't the end of all decisions. Even in the quasi-fascist regime he has built. He has no big red button that says 'nuke iran.' He has a guy with briefcase that generates codes. He then calls and orders a person, using that code, to nuke iran. Who has to relay that order (and whatever secret steps involved) to someone else, who has to nuke Iran. And that's the easy one, assuming they use an ICBM. If they go ship based or aircraft-based nuke there are DOZENS of people required to all agree, without reservation, to nuke Iran. That that's clearly the best option. That that is a legal order they are willing to bet the rest of their life and career on. Because if they carry out an illegal order, they are personally liable.

Nuking Iran, under all current laws, is illegal. Even if the president directly orders it. Any and all military personnel involved, at least 6, up to DOZENS, would all have to actively follow an illegal order, betting that by following the order TRUMP ET AL WILL NEVER LOSE POWER FOR THE REST OF TIME.

Do you know the type of person that gets to the point of commanding a nuclear submarine? A flight deck commander that relays the order? The general that directs the silo?

They don't answer to presidents. They don't answer to the secretary of defense. They managed to avoid all legal pitfalls while building a career that sets them and their spouse up for life, and they generally tend to only be loyal to the constitution; because they would have been filtered long ago if they were loyal to a party or person.

It takes just one person refusing an illegal order to stop the nuke. Just one. The US military was explicitly designed that way, and its why the government spends so much money using propaganda on our own troops.