If it involves charging the President with crimes, and convicting him, the only process is outlined like I said (per the US Constitution, the US House of Representatives and the US Senate). There is no process for arresting him.
And then, of the three branches of government - Legislative, Judicial and Executive - the Military is directly under the control of the Executive Branch, the President being the Commander in Chief. It’s the President that orders the military, not the military that orders the President ... :-) ...
That’s pretty much all you need to know in a nutshell.
You are just not getting this. It’s not about charging the POTUS with a crime. It’s about locking up a dangerous person (known to be dangerous because of what is observed about his connections, intentions, and actions) BEFORE he can attack this country or its people. It’s about preventing great harm. The Constitution calls it providing for the “common defense”, and it is CONGRESS who is given that responsibility. Even to the specific point of making rules about captures on land or sea.
They have made those rules about captures. They are in the NDAA. Unless you show me where the NDAA says the POTUS can’t be captured if he is classified as an enemy combatant, then the military is to be at least as vigilant of him as of anybody.
Show me where the NDAA says the POTUS can’t be captured even if he’s found to be an enemy combatant.