1917 cloture rule, by which two-thirds (now three-fifths) of the Senate could vote to end debate. But even then, only thirty filibusters occurred between 1880 and 1917, according to political scientists Sarah Binder and Steven Smith. Filibuster use remained low through the late 1960s—in fact, between 1917 and 1959, the Senate saw an average of only one per congressional term.
