Congress investigates to learn how laws are working, to expose waste and misconduct, and to inform the public. Investigations can examine agencies, private companies, and even the President, and they are often the most visible part of congressional oversight. They are also among the most contested, especially when Congress and the White House are controlled by different parties.
This guide explains the legal basis for investigations, the tools committees use, the help they receive from watchdog agencies, the limits on their power, and the investigations that defined the practice.
Committees gather information through letters requesting documents, staff interviews and depositions, and public hearings. Most standing committees can issue subpoenas, often by the chair alone under current rules, and witnesses can be required to testify under oath, with false statements punishable as a crime. Special or select committees are sometimes created for major investigations, and committees with government-wide jurisdiction, such as the House Oversight Committee, can examine nearly any agency.
Congress began investigating almost immediately, examining a military defeat in 1792. In McGrain v. Daugherty in 1927, arising from the Teapot Dome bribery scandal, the Supreme Court held that the power of inquiry is an essential auxiliary to the legislative function, implied by Article I. Congress may investigate any subject on which it could legislate or appropriate money, which covers almost every part of the federal government.
An investigation must serve a legitimate legislative purpose and stay pertinent to it. In Watkins v. United States in 1957, the Court overturned a contempt conviction because the witness was not told how questions related to the inquiry. Witnesses may invoke the Fifth Amendment privilege against self-incrimination unless granted immunity. Presidents may assert executive privilege, which the Court recognized but limited in United States v. Nixon in 1974, and in Trump v. Mazars in 2020 the Court set a test balancing Congress's needs against the separation of powers for subpoenas of a President's personal records.
If a witness refuses a subpoena, the committee and then the full chamber can vote to hold the witness in contempt. Under a law dating to 1857, the case is referred to a U.S. attorney for prosecution, though the Justice Department rarely prosecutes executive branch officials acting on a President's instructions. Congress can also file a civil lawsuit to enforce a subpoena, which can take years. Two former White House advisers were convicted of criminal contempt in 2022 and 2023 for defying subpoenas from the January 6 committee.
Congress relies on agencies that investigate on its behalf. The Government Accountability Office audits programs and reports to Congress, the Congressional Research Service provides analysis, and inspectors general inside agencies must report serious problems to Congress. Whistleblowers inside agencies are protected by law when they report wrongdoing to Congress, and their disclosures have launched many investigations.
Teapot Dome in the 1920s exposed bribery in oil leases. The Senate Watergate Committee in 1973 uncovered the White House taping system, leading to the President's resignation. The Church Committee in 1975 and 1976 revealed intelligence abuses and produced permanent intelligence committees and the Foreign Intelligence Surveillance Act. Later inquiries examined Iran-Contra, the September 11 attacks, and the January 6, 2021, attack on the Capitol. Supporters say investigations are essential to accountability, while critics argue that many have become partisan exercises aimed at the next election.
See how committees are organized in congressional committees explained, explore the ultimate check in impeachment explained, or meet the watchdogs in federal watchdogs.