Cloture

The Senate has no general rule allowing a simple majority to end debate. Cloture is the exception: a petition signed by sixteen senators, ripening after an intervening day, and then a vote that requires three-fifths of the full Senate, which is sixty votes when there are no vacancies. Only after cloture is invoked does the chamber move toward a final vote.

This is why sixty rather than fifty-one is the number that governs most Senate legislation, and why a bill with majority support can fail without ever receiving a vote on its merits. The modern practice rarely involves continuous speech; the mere threat of extended debate is enough to force the sixty-vote threshold, which is what commentary means by a filibuster.

Important categories are exempt, and knowing which ones explains a great deal of Senate behaviour. Nominations require only a simple majority, as do measures moving under budget reconciliation or a resolution of disapproval under the Congressional Review Act. Those exemptions are precisely why so much consequential legislation is routed through them.