The Filibuster debate and the requirement that approval of two-thirds of Senators (67) is necessary to change the body’s rules

http://www.bostonreview.net/BR38.1/charles_fried_frederick_schwarz_filibuster_constitution.php

“Even vice presidents have agreed. Although often overlooked, one of the duties of the vice president is to act as president of the Senate, including issuing advisory opinions about internal Senate procedure. Vice Presidents Nixon, Humphrey, Rockefeller, and Cheney all confirmed the inherent constitutional power of a majority of Senate members to enact rules changes.

As Nixon described it: “The right of the current majority of the Senate at the beginning of a new Congress to adopt its own rules cannot be restricted or limited by rules adopted by a majority of the Senate in a previous Congress.”