who has the power to issue a subpoena
Contempt of Congress Congressional rules empower all its standing committees with the authority to compel witnesses to produce testimony and documents for subjects under its jurisdiction. Committee rules may provide for the full committee to issue a subpoena, or permit subcommittees or the chairman (acting alone or with the ranking member) to issue subpoenas.
Impeachment in the United States At the federal level, Article Two of the United States Constitution states in Section 4 that "The President, Vice President, and all civil Officers of the United States shall be removed from Office on Impeachment for, and conviction of, Treason, Bribery, or other High Crimes and Misdemeanors." The House of Representatives has the sole power of impeaching, while the United States Senate has the sole power to try all impeachments. The removal of impeached officials is automatic upon conviction in the Senate. In Nixon v. United States (1993), the Supreme Court determined that the federal judiciary cannot review such proceedings.