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When Congress Comes Calling:a Primer on the PrinCiPles, PraCtiCes,and PragmatiCs of legislative inquiry

http://www.constitutionproject.org/wp-content/uploads/2012/09/175.pdf

excerpt:
Throughout its history, Congress has engaged in oversight of the Executive Branch—the review, monitoring,and supervision of the implementation of public policy. Congress’ right of access to executive branch information is constitutionally based and is critical to the integrity and effectiveness of our scheme of separated but balanced powers. The first several Congresses inaugurated such important oversight techniques as special investigations, reporting requirements, resolutions of inquiry, and use of the appropriations process to review executive activity. The legislature’s capacity and capabilities to check on and check the executive have increased over time. Public laws and congressional rules have measurably enhanced Congress’ implied power under the Constitution to conduct oversight.