During the Vietnam war there was a retired general ( forgot his name ) who came out against the war. The government tried but couldn’t do anything to stop or punish him.
CNN is supposedly planning some fake “Town Hall” with Mattis and Kelly. It’s one thing to be against the war. It’s another to directly attack POTUS on medical grounds or whatever nonsense they come up with.
I think you might be referring to Major General Edwin Walker. He was a thorn in the side of Presidents Eisenhower, Kennedy, and Johnson. He tried to resign his commission under Eisenhower but the resignation was refused. It was later accepted by Kennedy. By resigning, he gave up all benefits of a 30 year career, including his retirement pay, therefore, he was not subject to military discipline. At that time, he was the only General Officer in history to have resigned his commission and probably is still the only one.