Yeah, that would be hard to defend as first amendment retaliation.
/s
They were clever enough to precisely say only what is exactly taught to troops in Law of Armed Conflict training. They've got advisory lawyers, too. A charge for what they actually said would look silly to a court-martial.
"We know what you did, but we can't prove you did it."
Edit:
But worse: The military justice system takes "command influence"
extremely seriously. When I say "extreme," I mean to the point of near absurdity. "Command influence" means nobody in the chain of command can do or say anything, however slight, that might influence the administration of military justice.
Nobody, including the president, and they are gosh-darned serious about that. Military discipline depends on it, and military discipline is the only reason the military justice system exists.
Remarks by Obama actually caused military judges to severely restrict possible sentences in two courts-martial that were ongoing at the time he made his remarks. Obama said persons under such accusations should be dishonorably discharged, and as a direct result the two judges ordered that they could
not receive punitive discharges.
If Trump makes such statements, it would have the same effect in any subsequent courts-martial.