The military is so Dug in to Washington DC There is no way they are there just for a one day inauguration which is only two hours long. They have cut the streets up installed pop-up spikes prevent cars Running past the checkpoints.
They have created tunnels for the cars to go through that are too small or a Humvee or a tank.
They are there to stay for a while. The question is, are they there for Donald Trump or Joe Biden?