On March 8, 1917, the U.S. Senate adopted the cloture rule to limit filibusters. Under Rule 22, two-thirds of Senators could vote to close debate on a given bill, thereby ending an ongoing filibuster. In 1975, that number was lowered to three-fifths of the Senate, which amounts to sixty Senators.



Read a history of filibuster and cloture from the archives of the U.S. Senate.