There is very little scope to disobey a direct order from the president. Disobeying the order and committing treason will only briefly delay the execution of the order as it's passed down to the next in line fallback.

Specifically where nuclear strikes are concerned, a lot of planning has gone into maximising the probability of compliance. Missile combat crew carry a sidearm to threaten their counterpart with death if they refuse to act on an authenticated launch order. They wear 4 point harnesses during launch sequence, primarily as a psychological device to prevent them from getting up and walking away mid sequence if their conscience gets the better of them, etc.

If trump or any other president said launch, there would be a launch.

Correct me if I'm wrong, but they also do "dry run" launches where the crew themselves don't know whether or not it's a drill, right? So they could safely assume that the real thing is also one of the regular, unscheduled drills.

Guess you didn't see Wargames? 8-)

It's not about conscience, though. It's about you or at least many of your friends and family either burning or starving to death. That's the thing about MAD: It's mutual.

For all the missile guys know, the Russian missiles are already in the air. Nobody's likely to tell them it's a first strike.

Yeah, but there's an entire chain of command. I have a hard time believing that all the generals will go along with starting a nuclear war.

They don't all have to go along. See the "execution" section- only a couple of senior officers have to authenticate the President, and issue the order electronically. At that point only one chain between them and a launch crew have to obey the orders to launch. The whole process is meant to only take a few minutes.

https://en.wikipedia.org/wiki/Single_Integrated_Operational_...

Everyone involved in the chain is part of the Personnel Reliability Program. It's mostly to make sure someone doesn't launch without an order but also probably to make sure that they will follow orders, including launch orders.

https://en.wikipedia.org/wiki/Personnel_Reliability_Program?...

I read somewhere that the Sec. of Defense has to agree with it.

Only five minutes would elapse from order to launch, even if a significant number of people throughout the chain to refuse the order.

Ultimately if the President orders the launch, it will happen. And it's the President's decision alone.

https://www.bloomberg.com/politics/graphics/2016-nuclear-wea...