'This is a nation of constitutional law, not of martial law.'—Judge Karin Immergut

The “state of exception” is a concept that goes back to the Roman Empire. The Senate could suspend their role in times of extreme threat to the Empire, and appoint a dictator who could control the armies and determine all actions of government until the crisis passed, and the Senate reasserted its authority. This is how Caesar Augustus became Emperor Augustus, and it’s the source of Brutus’s actions in Shakespeare’s play.

That’s the tl;dr version.

Several governments in Europe still incorporate a “state of exception” along the Roman model in their laws. It’s a paradoxical situation that intrigues political scientists and legal scholars. But there is no such provision in Anglo-Saxon jurisprudence, nor in its legal history. That’s partly because of the long history of monarchs, but the upshot is, “martial law” is not a legally recognized exception to the unwritten British constitution, nor to the American one. In the former, it would usurp the rule of even the monarch. In the latter, it would usurp the rule of we, the people. There is no constitutional provision that allows any person or persons to arrest the rule of law and to rule as they see fit in whatever circumstances exist. “Martial law” is molar; not under our constitutional system. It’s one of those ideas that appeals to fiction writers composing apocalyptic scenarios, but in reality it’s a shibboleth at worst, a chimera at best. In American law, it is an utter delusion.

Yes, under federal law the President can nationalize the National Guard and order them to take actions in specific places. But as Judge Immergut ruled, that determination arises from facts and law, not Presidential fiat and unfounded ignorance. Under the general principles of federalism (and the specific rule of Posse Comitatus), the President cannot send NG troops, or military forces, where he wills, without regard for state sovereignty. Just like throwing around the word “terrorist” doesn’t allow the President to suspend the rule of law, declaring a collapse of social order where there is none doesn’t establish grounds for federalizing NG soldiers.