The dearth of debate limitations in Senate rules creates the possibility of filibusters. Individual Senators or minority groups of Senators who adamantly oppose a bill or amendment may speak against it at great length, in the hope of changing their colleagues' minds, winning support for amendments that meet their objectives, or convincing the Senate to withdraw the bill or amendment from further consideration on the floor. Opposing Senators also can delay final floor action by offering numerous amendments and motions, insisting that amendments be read in full, demanding roll call votes on amendments and motions, and a using a variety of other devices.
The only formal procedure that Senate rules provide for breaking filibusters is to invoke cloture under the provisions of paragraph 2 of Rule XXII. However, cloture cannot be voted until two days after it is proposed, and a simple majority of the Senate is insufficient to invoke cloture. Cloture requires the support of three-fifths of the Senators duly chosen and sworn, or a minimum of 60 votes (unless the matter being considered changes the standing rules, in which case cloture requires a vote of two-thirds of the Senators present and voting). For this reason alone, cloture can be difficult to invoke and almost always requires some bipartisan support. In addition, some Senators are reluctant to vote for cloture, even if they support the legislation being jeopardized by the filibuster, precisely because the right of extended debate is such an integral element of Senate history and procedure.
Even if the Senate does invoke cloture on a bill (or anything else), the result is not an immediate vote on passing the bill. The cloture rule permits a maximum of thirty additional hours for considering the bill, during which each Senator may speak for one hour. The time consumed by rollcall votes and quorum calls is deducted from the thirty hour total; as a result, each Senator does not have an opportunity to speak for a full hour, although he or she is guaranteed at least ten minutes for debate. Thus, cloture does not stop debate immediately; it only ensures that debate cannot continue indefinitely. And even the thirty hours allowed under cloture is quite a long time for the Senate to devote to any one bill, especially since Senators may not be willing to invoke cloture until the bill already has been debated at considerable length.