The Lincoln Conspirators were the first civilians to be tried by a military tribunal. None has occurred since then to my knowledge. According to military law, civilians may be tried by the military when Martial Law is in place. It remains to be seen if they will actually be tried by the military, perhaps just legally processed by military lawyers, then referred to City/Federal courts for trial and sentencing. I can see the RATS getting on this hot and heavy with the courts, depending on how it’s handled. Trump should just declare Martial Law in D.C., and all the other cities he plans to clean up for the duration Federal troops are involved. Then the military can be involved throughout the whole process to its end. But of course the RATS would sue over that too.
This explains precisely when military tribunals can be used for civilians. Graham questioning Kavanaugh at his hearing.
https://www.youtube.com/watch?v=oOAkU_4iPYA
Graham asks Kavanaugh about Military Tribunals