Matt Bai’s use of “Commander in Chief” in his article Taking the Hill seems kind of odd being that the POTUS is actually the Commander in Chief of the military, Head of Government, Head of State, etc.

“Having served under seven commanders in chief during his time in the Senate, Biden understands as well as anyone the pervasive fear in Congress that presidents are out only for themselves.”

New York Times

Didn’t Biden, as a Senator, simply serve under seven Heads of Government? Commander in Chief is really used as a catch all for all the roles of the Office of President of the United States.