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Marine Security Guard Battalion
Marine Security Guards provide security services to selected Department of State Foreign Service posts to prevent the compromise of classified material and equipment and to provide protection for United States citizens and United States Government property. The Marine Security Guard Battalion exercises command, less operational control, of these Marines, in that it is responsible for their training, assignments, administration, logistical support, and discipline.
The origins of the modern MSG Program began with the Foreign Service Act of 1946 which stated that the Secretary of Navy is authorized, upon the request of the Secretary of State, to assign enlisted Marines to serve as custodians under the supervision of the senior diplomatic officer at an embassy, legation, or consulate. Using this Act, the DOS and Marine Corps entered into negotiations to establish the governing provisions for assigning MSGs overseas. </TD></TR></TBODY></TABLE>
http://www.globalsecurity.org/milita...usmc/msgbn.htm
From what i understand Presidental Security is mainly the Secret Service's responsiblilty, however they will be supported by ANY other enforcement agency