The chairman of the Joint Chiefs of Staff
The chairman of the Joint Chiefs of Staff (CJCS) is the highest-ranking and most senior military officer in the United States Armed Forces  and is the principal military advisor to the president, the National Security Council,  the Homeland Security Council,  and the secretary of defense.  While the chairman of the Joint Chiefs of Staff outranks all other commissioned officers, the chairman is prohibited by law from having operational command authority over the armed forces; however, the chairman does assist the president and the secretary of defense in exercising their command functions. 
The chairman convenes the meetings and coordinates the efforts of the Joint Chiefs of Staff (JCS), an advisory body within the Department of Defense comprising the chairman, the vice chairman of the Joint Chiefs of Staff, the chief of staff of the Army, the commandant of the Marine Corps, the chief of naval operations, the chief of staff of the Air Force, the chief of space operations, and the chief of the National Guard Bureau.  The post of a statutory and permanent Joint Chiefs of Staff chair was created by the 1949 amendments to the National Security Act of 1947. The 1986 Goldwater–Nichols Act elevated the chairman from the first among equals to becoming the “principal military advisor” to the president and the secretary of defense.
The Joint Staff, managed by the director of the Joint Staff and consisting of military personnel from all the services, assists the chairman in fulfilling his duties to the president and secretary of defense, and functions as a conduit and collector of information between the chairman and the combatant commanders. The National Military Command Center (NMCC) is part of the Joint Staff operations directorate (J-3).
Although the office of Chairman of the Joint Chiefs of Staff is considered very important and highly prestigious, neither the chairman, the vice chairman, nor the Joint Chiefs of Staff as a body has any command authority over combatant forces. The Goldwater–Nichols Act places the operational chain of command from the president to the secretary of defense directly to the commanders of the unified combatant commands.  However the services chiefs do have authority over personnel assignments and oversight over resources and personnel allocated to the combatant commands within their respective services (derived from the service secretaries).
The chairman may also transmit communications to the combatant commanders from the president and secretary of defense  as well as allocate additional funding to the combatant commanders if necessary.  The chairman also performs all other functions prescribed under 10 U.S.C. § 153 or allocates those duties and responsibilities to other officers in the joint staff under his or her name.
I submit the Wikipedia definition as Exhibit A as to why General Milley is no longer worthy of the position of trust which he was appointed.
On more than one occasion General Milley has allowed partisan politics to skew the execution of his office and position as the principal military advisor to the president. In the latter days of the Trump administration he began distancing himself from the president and allowed outside forces to come between him and his commander in chief.
The first noticeable act was after President Trump went to a church in DC and held up a bible emphasizing God as the supreme ruler. When Congressional Democrats and the media began rumbling about Trump General Milley pulled away and was seen visibly walking behind the president.
Another act of resistance by General Milley was when he sided with House Speaker Pelosi in failing to insure federal troops were sent to secure the Capital prior to January 6th 2021. That was followed by a congressional inquiry from Speaker Pelosi directly telling General Milley not to follow orders from the president and keep him away from the “nuclear football” at all cost.
The fact that General Milley took the phone calls from the congresswoman shows clear intent on his part to forsake his duty as Chairman of the Joint Chiefs of Staff and allowed her to influence and tarnish the trust placed in him by the president.
I don’t understand why the Secretary of Defense did not voice himself in this matter as General Milley is the senior military member of the Department of Defense.
When it comes to military protocol, tradition and the Uniform Code of Military Justice there is no room for what amounts to insubordination or insurrection at the highest level, the inner circle, of the presidential administration.
I understand that general officers take two oaths, one as a commissioned officer and one the oath of office which is to defend the Constitution against all enemies. Never have I seen petty politics being on prominent display by active duty general officers whose demonstrated hatred for a president.
It would have been better for General Milley to resign his post, and choose retirement over politics. His choice to stay was not the better one. – I am the Real Truckmaster!