Besides trump himself Pete Hegseth is the boss of the entire military. Unless you are Trump then Hegseth is the most powerful person in the world

This gives him the right to simply censure Mark Kelly if Hegseth believes he broke the military rules. Hegseth is the boss of the entire military he can just do that

But Kelly will not lose his pension until they go through a lengthy and complicated legal process where probably at least 1 judge will decide if Hegseth is full of shit, which he obviously is