John Randolph Thune is an American politician serving as the senior United States senator from South Dakota, a seat he has held since 2005. Thune is in his fourth Senate term and is the Senate minority whip, a post he has held since 2021. A member of the Republican Party, Thune served three terms as the U.S. representative for South Dakota's at-large congressional district from 1997 to 2003.

The United States Senate is the upper chamber of the United States Congress. The United States Senate and the lower chamber of Congress, the United States House of Representatives, comprise the federal bicameral legislature of the United States. Together, the Senate and the House maintain authority under Article One of the U.S. Constitution to pass or defeat federal legislation. The Senate has exclusive power to confirm U.S. presidential appointments, approve or reject treaties, and try cases of impeachment brought by the House. The Senate and the House provide a check and balance on the powers of the executive and judicial branches of government.