My sincere hope is that should he be stupid enough to try something like that there would be no “marshals” willing to enforce it.
Anyway, martial law is only imposed to keep order in an area of unrest, it would not work for a country the size of the US. I doubt that many generals would be willing to commit their forces to impose such an order over the entire country. That is what they do in small banana republics not in a country the size the US.