Minor dig on President's special relation to the Marine Corp.
Marines protected president back in the day because they were stationed in DC prior to boarding ships.
Interesting info from article:
One last comment after Yorktown in 1781, the revolutionary war did not end till 1783. Congress failed to pay the troops, thus whole regiments under Washington marched in the Capital, then Philadelphia. These marches were stopped by Washington, but just barely for the troops had support even among the officers. Given this was an attack on Congress (Washington was just a General working under the authority of Congress at that time, a Congress that could fire him at any time, unlike when he was President starting in 1789).
Thus, the US Army can not claim being “Always Faithful” for the Army does not have that record, the Army has marched on Congress, something the other services can say they never did. That history was one off the reason Marines were preferred by Washington over Army Troops in the 1790s.
https://www.quora.com/Why-are-the-Marines-the-only-branch-shown-to-guard-the-President
National Security Act of 1947 defines the Marine Corp role.
"The United States Marine Corps, within the Department of the Navy, shall include land combat and service forces and such aviation as may be organic therein. The Marine Corps shall he organized, trained, and equipped to provide fleet marine forces of combined arms, together with supporting air components, for service with the fleet in the seizure or defense of advanced naval bases and for the conduct of such land operations as may be essential to the prosecution of a naval campaign. It shall be the duty of the Marine Corps to develop, in coordination with the Army and the Air Force, those phases of amphibious operations which pertain to the tactics, technique, and equipment employed by landing forces. In addition, the Marine Corps shall provide detachments and organizations for service on armed vessels of the Navy, shall provide security detachments for the protection of naval properly at naval stations and bases, and shall perform such other duties as the President may direct: Provided, that such additional duties shall not detract from or interfere with the operations for which the Marine Corps is primarily organized. The Marine Corps shall be responsible, in accordance with integrated joint mobilization plans, for the expansion of peacetime components of the Marine Corps to meet the needs of war."
Not sure if this duty to perform special assignments for POTUS is special, but it appears to be so, despite him being CINC and ultimately the leader of the Armed Forces.
https://www.mca-marines.org/gazette/marine-corps-and-national-security-act