This was a failure of monumental proportions, and now we are reaping the poisonous harvest.
Declaring martial law is akin to declaring civil war. I am not even sure the US military will obey the orders at this point, because the DoD knows the courts will not back the legality of the orders.
Therefore, to act under the President's authority would make them subject to criminal penalties, imprisonment, and war crimes charges themselves.
The time to act was 4 years ago. We had nice rhetoric about "draining the swamp" - but that's all it was.