Final answer:
To end a filibuster in the U.S. Senate, a cloture motion must be passed with a supermajority of 60 votes. This cloture motion enables the Senate to end debate on a bill and move forward to a vote, and the threshold for cloture has historically been lowered from two-thirds to three-fifths of the Senate.
Step-by-step explanation:
The Senate and the Filibuster
The subject in question is the mechanism that the U.S. Senate uses to end a filibuster. A filibuster can be described as a parliamentary procedure where senators delay a vote on a proposed piece of legislation by extending debate. According to Senate rules, a filibuster can only be ended through a cloture motion. A cloture motion requires a supermajority to pass—specifically, 60 out of 100 senators must vote in favor of the motion to end debate and proceed to a vote on the legislation. Over time, the requirement for a supermajority to invoke cloture has given significant power to the Senate minority to obstruct legislation.
In historical context, the Senate filibuster has been a tactic used since the 19th century, designed to allow prolonged debates and thus delay or block the passing of legislation. The cloture rule has evolved, with the threshold lowered from a two-thirds majority to the current three-fifths, or 60 votes, in 1975. This was a response to increased partisanship and was intended to streamline the legislative process while still maintaining the ability for extended debate. Unlike the traditional filibuster, where actual prolonged speeches were made, in modern times the mere threat of a filibuster often suffices to influence legislative action, as bills unlikely to meet the cloture threshold are typically not even brought to the floor.