Earlier quoted context omitted.
The "states" national guard can be federalized at a moment's notice. The president need only give the order and put his signature on it. At that point, they report to the President and no one else. This isn't theory, Alabama's was federalized some time when my dad was a kid. The president never rescinded the order.
De jure doesn't matter when the law has been tossed aside. The loyalties of the individuals, units, officers will choose sides on their own. I'm not holding my breath on the military being willing to enmass defect against an authoritarian though.
Historically, that's an important consideration in military loyalty under contested scenarios.