I retired after 26 years. I am telling you that the military will follow orders, short of killing American civilians, and I am not entirely sure of that.
Troops fired on Kent State students.
Military advisors were at the branch Davidian Compound. Military at the Ruby Ridge massacre along with law enforcement.
Entire divisions stacking arms? Now you are being naive. Field and especially general grade officers are political, meaning their survival comes first.
Remember Tonkin Bay ? Military and civilian should have gone to prison over that. Northridge Operation, same thing. And these were general grade officers.
Bottom line, If Obama issues an illegal order, CINC will step in.