And there is this link:
The cloture rule was implemented in 1917, on a bipartisan 76-3 vote. (p226). With the concurrance of 2/3rds of the Senators voting, debate would be limited and taking the vote would be set for a time certain.
In 1949, on a 63-23 vote, the threshold was modified to 2/3rds of the Senators duly chosen and sworn. (p229).
In 1959, a 77-22 vote made cloture possible with 2/3rds of the Senators present and voting. (p247). Also, cloture was broaded to include rules changes - this is where the "2/3rds of Senators present and voting are required to change the rules" rule comes from. The 1959 changes are referred to as the "Johnson (LBJ) Compromise."
In 1975, Senator Pearson introduced a proposal to change the threshold to 3/5ths of Senators present and voting. (p257). That proposal did not pass. In the same year, Senator Byrd's proposed revision to 3/5ths of all Senators passed on a 56-27 vote. (p259).
http://www.law.harvard.edu/students/orgs/jlpp/Gold_Gupta_JLPP_article.pdf
Slightly improved version here .. points out relationship (and links) to Robert's Rules of Order.
Senate Rules from 1789 to 1806 permitted calling the question with a simple majority. See http://rules.senate.gov/history.html, Rule IX. This rule was removed in 1806, and in its place was a requirement to obtain unanimous consent to move to the vote. One objecting Senator could stifle the vote.
The cloture rule was implemented in 1917, on a bipartisan 76-3 vote. (p226). With the concurrance of 2/3rds of the Senators voting, debate would be limited and taking the vote would be set for a time certain. This matches the procedure in Robert's Rules of Order.
In 1949, on a 63-23 vote, the threshold was modified to 2/3rds of the Senators duly chosen and sworn. (p229).
In 1959, a 77-22 vote returned to the original 2/3rds of the Senators present and voting. (p247). Also, cloture was broaded to include rules changes - this is where the "2/3rds of Senators present and voting are required to change the rules" rule comes from. The 1959 changes are referred to as the "Johnson (LBJ) Compromise."
In 1975, Senator Pearson introduced a proposal to change the threshold to 3/5ths of Senators present and voting. (p257). That proposal did not pass. In the same year, Senator Byrd's proposed revision to 3/5ths of all Senators passed on a 56-27 vote. (p259).
http://www.law.harvard.edu/students/orgs/jlpp/Gold_Gupta_JLPP_article.pdf