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
I wander if there still wouldn't be a way out of this mess, even with the agreement in place.
What if, with the announcement of a cloture vote, there would simply be a requirement that the vote of 2/5ths of seated Senators would be needed to deny cloture, along with the 50 needed to maintain a quorum.
This preserves the filibuster option, but puts the pressure on the minority to keep at least forty members in the Senate chamber at all times and keep talking. As soon as there is a quorum and 40 members of the minority are not present, cloture could be invoked. So, for example, a vote of 11 for cloture and 39 against would result in closing debate and scheduling a vote on the issue. In addition, the rule could also say that at whatever point there is no one to continue debate, cloture is automatically invoked. If the Republicans did this, they could "preserve" the filibuster but place all the burden on the Democrats to keep almost their entire caucus there at all hours. Republicans would only need to keep 10 or 11 in chambers in the waiting game. This allows the rest of the Republicans to hit the talk shows, etc.
Since this is not the original constitutional option, the 7 would be free to vote for this rule change. This would restore Senate tradition, preserve the filibuster, all the talking points of the Democrats. But it would prevent them from sustaining it forever and they would have to fold at some point.
What do you all think?