The Marines have a special charter to perform any missions that are dictated by the President.
No more than any military unit would. No 'special' charter. HMX flies the President and others around.
As outlined in 10 U.S.C. § 5063 and as originally introduced under the National Security Act of 1947, three primary areas of responsibility for the Marine Corps are:
- Seizure or defense of advanced naval bases and other land operations to support naval campaigns;
- Development of tactics, technique, and equipment used by amphibious landing forces in coordination with the Army and Air Force; and
- Such other duties as the President or Department of Defense may direct.
Sure, the President is the CoC of all of the military. But this special designation is embedded in Title 10 of US Code.
Q hinted at this on several occasions, and asked people to think why it was necessary.