In the Nuremburg trials the orders given to soldiers were "legal", in Germany. They found that soldiers need to meet a higher level of responsibility than just what is legal and lawful in one's own country. I can think of what would almost certainly be an illegal order in the U.S. military. If your Sergeant ordered you to kill a fellow solider that was sitting there, no weapons, just sitting there shooting the breeze, that would surely qualify as an illegal order and if a man followed it he would have no excuse. It appears that the soldiers were ready to react if Trump ordered an illegal nuclear strike on China. And though the President has wide ranging power a nuclear strike on a country that had not attacked us would almost certainly qualify as an illegal attack in the US as well.
Yes, I agree, and I would think that soldiers who are at least literate and have at least a high school education, as well as a good upbringing and good moral foundation, they would certainly have moral standing in refuse to obey an order to commit murder. They were, at the very least, aware of the Hague Convention and the Geneva Convention, as well as treaties such as the Kellogg-Briand Pact. I think they knew full well that their only chance of evading any form of prosecution or retribution for their crimes was for Germany to win the war. That's one reason that the whole "just following orders" defense didn't really convince anyone.
It's a good thing our generals and other military personnel take an oath to the Constitution. In Germany, they took an oath to the Führer.
It seems to be an interesting topic in some fictional stories, such as in the opening scene of
Wargames where the missile commander thought he was about to kill 20 million people, and he just couldn't bring himself to turn the key to launch the missiles.
Another interesting story was
By Dawn's Early Light, which is set in 1990, and the Soviets launched a nuclear strike on America by mistake. The president's helicopter, which was on its way to Andrews to meet with Air Force One, had crashed and the president was presumed killed (however he survived and was taken to a FEMA medical facility).
The VP and rest of the cabinet were also dead or presumed, except for the Secretary of the Interior, who was the only surviving cabinet member and on a fact-finding trip in Louisiana when all this was happening. So, he was considered the president and commander-in-chief at that point. The war had escalated and a Navy admiral was trying to convince to slow things down and try to stop the escalating nuclear exchange, but was still relatively even and only hit direct military targets, not yet the major cities. The new president was concerned about "losing the war" and felt that "winning is everything." The admiral was trying to be polite, but growing impatient with this guy who was clearly not cut out to be making these kinds of decisions. Also at the conference table was Col. Rip Torn, who was also kind of a crazoid, who offered another suggestion to the president, which involved sending all the remaining bombers to Russia on a "grand tour" to bomb all their major cities and installations. The admiral thought it was "madness," and he knew that the Soviets would come in and wipe out our cities as well.
It was at that point that they got communication that the real president was still alive, but injured and blinded, yet still lucid and awake enough to make decisions. They were able to intercept the fake president and give new orders to the bombers and subs to cease hostilities.
Sorry, I didn't mean to go into a whole movie plot, but the overall topic of the president's authority over nuclear weapons and the processes into carrying out presidential orders is kind of fascinating.