Posse comitatus.
By the way, this may form part of the plan for graduated martial law implementation, but we’ve been pretty far down that road already. The Civil War and reconstruction went all the way. The National Guard has been nationalized who knows how many times for use in what are ostensibly state issues. Most famously to enforce desegregation, though that was an edict from the federal courts. Also for piddling crap like the Rodney King riots.
The DEA, FBI, ATF, etc. are technically paramilitary outfits, but I don’t see any good reason to think of them as anything but military.
In an admittedly small way, but worth a mention here, is what Gov "mini-me" did PRIOR TO the blizzard that hit a couple of months ago here in MA. With the hardest to be hit Cape, nearly nada to fall in the Berkshires, and BEFORE a single flake had fallen, the subjects of the Peoples Republic here were forbidden by law from driving, from one end of the state to the other. The bulk of the storm was from midnight to 5 AM, when very few would be on the roads anyway, during the period when plows need to and did do their thing. But, that didn't stop this writ by our king to outlaw anybody on the road from 4 PM thru much of the following day.... even in the Berkshires where an inch or two fell.
Obviously, this was not martial law; BUT, it was the first time since 1978 such a ban was put in place. Unlike 1978, which was put in place due to a current demonstrated need, the bliz of 2013 was put in place prior to a single flake early in the day, for 4 pm, for a storm that didn't even start with the 1-2" per hour stuff till midnight. This has gotta be a fine example of incrementalism...
Thanks for bringing that up. I doubt any one in today's DoD or WH knows what that means. We will need to gently remind them.