Answer:
Department of State
Explanation:
The Executive Branch and the Congress are backed up by law and they have the constitutional responsibilities for U.S. foreign policy.
Within the Executive Branch, the Department of State is the  responsible for leading U.S. foreign affairs agency, and the Secretary of State is the President's principal foreign policy adviser. The Department pursues or advances U.S. objectives and interests and they also supports the foreign affairs activities of other U.S. Government entities including the Department of Commerce and the U.S. Agency for International Development and also execute other duties.
