The US Military will shatter if ordered into US Cities against US Citizens unless a catastrophic event causes it. The Military will not enforce Martial law simply because some President orders it. NDAA or NO NDAA. Such a move would cause a civil war to erupt, with some units following orders while others did not. And even among the Units trying to follow orders there would be desertion and sabotage. With troops and Officers refusing to comply. The event that would not shatter the Military would have to be Country wide for a Country wide Martial law to be followed. Even local events would have to be so catastrophic that the Military could not see the National Guard handling it successfully. I am a Delusional Paranoid that does not trust the Government but I spent 16 years in the Marine Corps and studied lots of military history. There is no way the Military enforces Martial law with out something being so catastrophic they feel there is no other way. Even then I suspect some dissent would occur.