Depends on how he cows them into subservience. If he uses the threat of electoral defeat for opposing him, that's totally legitimate. If he uses his position as commander in chief to threaten them with force, that's different.

It does not matter how. The fact that he is able to do it at all illustrates a design weakness. Until recently, Presidents chose (consciously or otherwise) not to exploit that weakness. It doesn’t mean the weakness wasn’t always there.