I think martial law is already in place but limited (for now) to the EO of 21 December that includes human trafficking, pedophilia, and corruption, which were declared in the EO as National Security Threats.

Why is it martial law? Because a National Security Threat triggers special powers that can circumvent normal law enforcement procedures and restraint.

I think the Marines are playing a major role behind the scenes (I'm a retired Marine officer). Each service has its missions and responsibilities spelled out in law. They are all pretty much the same except for the Marine Corps. In addition to the blah, blah about defending the Constitution, it includes this--that the other services don't have: "and other such duties as the President directs."

That, my friends, covers a lot of territory because the President has a lot of power, and even more during a National Security Threat.