Nothing in subsection (a)(3) of this section shall be construed to preclude or limit in any way the authority of the United States Secret Service to provide protective services pursuant to section
3056 or
3056A of title
18 at a level commensurate with protective requirements as determined by the United States Secret Service. The Secretary of State, the Attorney General, and the Secretary of the Treasury shall enter into an interagency agreement with respect to their law enforcement functions.