then with the nuclear codes, he could order a strike against the US without any help from the current US military who would never participate, but then Obama would not need their help.
No way this will fly.
ONE: Few thousand people? Replacement will not happen overnight.
TWO: Training? You think the people that train others how to deploy and fire nuclear weapons wouldn't notice a boatload of melanin-enhanced trainees with attitudes?
THREE: You're pre-supposing that the executors of that National Command Authority (Generals, colonels, majors) would not immediately recognize this as a nuclear armed coup-d'-etat in progress and start resisting.
You make some good points in post 257.
I think the final point maybe that there may be a further failsafe that the public is unaware of (and maybe even potus is unaware of). That is it may take more than the missle operators and the president’s order and computer codes to fire the missles. It would be the final check and balance.
Nevertheless, this really is the only avenue for conquest of the US and that is from within and by potus and control of the US nuclear arsenal.