I feel like this assumes that "the police" or "the military" are monolithic organizations with unified purpose and a clear understanding and respect for the law. The military and the police are groups of people subject to external influence and internal conflict.

Say for example, that Trump were to make an illegal arrest order. Just "Arrest Nancy Pelosi" because of some imagined treason. Does Nancy Pelosi end up in jail that day? A LOT comes down to the opinions of the guy who hears the order in that moment. A lot comes down to the judiciary and the police or military brass after that.

This is the fear when people talk about the politicization of the DoJ and FBI. Those organizations should serve the law, not the president. But there seems to be an active effort to undermine that, and to view that as a quaint and naive view of a child. The modern view seems to be that every thing is political and that everything SHOULD be and further, that to pretend otherwise is a bad faith effort to conceal inescapable bias. I think the mainstreaming of this view is one of the more troubling likely legacies of Trump.