At noon on Jan. 20, the U.S. Marine who carries the “nuclear football” will begin following Biden, not Trump. The National Military Command Center will be operating off of nuclear launch codes that Biden possesses, not the ones Trump had in the morning.
The generals, even if Trump believes otherwise, will take their orders from Commander in Chief Biden.
This is all a severe way to think about it, but it’s an important way to think about government from time to time. What we have built in the U.S., with a rule of law, a constitution, a military, and a civil service, is a government that, even though it is ultimately based on guns and bombs, functions according to laws and the will of the people.
So, even if Trump manages to barricade himself in the White House somehow (which I seriously doubt considering that he obviously prefers Mar a Lago), he won’t be a usurper. He’ll be a mere trespasser.