Correct, which is why Mattis would be HVT #1 in a coup attempt.
Do you really think Mattis would give his word to Trump and then attempt a coup against him?
I really do not believe this warrior would stoop this low seeing that some sensibility is being restored to the rank and file. Plus he is an honorable man.
I do believe Mattis is the only person that would have Trump kowtowing to him and that has already happened on the issue of "extreme interrogation" (WETF that is). Which is good. I believe when it comes to the might of the US Military, you need a strong man between the President and the Armed Forces.