Those that categorically state there will be no military tribunals are suffering from normalcy bias. The tribunals are the remedy when the civilian courts are unable to function. If the enemy are able to create the level of chaos they are promising, then the military tribunals become a much more clear and present prospect.
And there is historical precedent-— the Lincoln Assassination Commission, and also the trial by another all military judiciary— the trial of the last commandant of the CSA’s Andersonville Prison (who was a Swiss citizen, btw— thereby showing that military tribunals can adjudicate anyone, in the correct legal setting).
Also see: Supreme Court Justice Kavanaugh’s exchanges under questions from Lindsey Graham at his Senate Judiciary Committee qualification/approval convening. We are...at War, still to this day, all the way from 2001 at a minimum.