Congressional Oversight

The Constitution never mentions oversight, but the Supreme Court has long held that the power to investigate is implied by the power to legislate. Congress's first investigation came in 1792, into the defeat of General Arthur St. Clair's army by a confederation of Native nations, and the House requested documents from the executive branch. In McGrain v. Daugherty in 1927, arising from the Teapot Dome scandal, the Court confirmed that Congress may compel testimony in aid of its legislative function.

Oversight takes many forms. Committees hold hearings, request documents, and issue subpoenas. The Government Accountability Office audits programs at Congress's request, the Congressional Research Service supplies analysis, and inspectors general, created in most agencies by the Inspector General Act of 1978, report to both their agency heads and Congress. Congress also oversees through the purse, attaching reporting requirements and limits to appropriations, and through the confirmation of officials. Landmark investigations include the Senate Watergate Committee in 1973, the Church Committee on intelligence abuses in 1975, the Iran-Contra hearings in 1987, and the House committee on the January 6, 2021 attack on the Capitol.

The power has limits. An inquiry must relate to a valid legislative purpose, cannot simply expose private affairs for its own sake, and must respect constitutional rights and executive privilege. In Trump v. Mazars in 2020 the Supreme Court set a heightened standard for congressional subpoenas of a President's personal records. Oversight tends to intensify sharply under divided government, when the party controlling a chamber differs from the President's, and to recede under unified government.