Senate rules require 67 votes to change the rules of the Senate. However, it’s actually quite possible for 50 Senators—if backed by the Vice President—to have elements of existing procedural deemed unconstitutional. The US court system neither will nor should rule on things like the constitutionality of a de facto supermajority rule. But this is precisely why you have a President of the Senate (i.e., a Vice President) and I think it would be perfectly plausible for Joe Biden to say that by specifying supermajority voting for certain purposes (treaties, veto overrides, constitutional amendments) the constitution is clearly assuming majority rule for other purposes. Then it would take a majority of Senators to back up Biden’s ruling. And low and behold, a return to majority rule.
Yesterday, Harry Reid damped hopes for this kind of reform by stating that in his view it takes 67 votes to change the rules.
My take on this is that it’s always been extremely unlikely that the filibuster would be curbed through the majoritarian process. Nevertheless, the way you get to reform is through a credible majoritarian threat. If you look at the successful 1975 filibuster reform you’ll see that this is how it went down. Reform opponents feared that reformers were getting close to pulling the trigger on filibuster-elimination, so they formed a compromise proposal. That’s how we got to 60 down from 67. Similarly, during the 2005 standoff it was the existence of a credible “nuclear option” threat that got Democrats to allow the confirmation of Bush’s judges.
If people think it’s plausible that 50 Democrats will band together and eliminate the filibuster in 2011, then I think it’s likely you’ll get 67 votes for some kind of phase-out proposal that would be friendlier to the interests of the Republicans. But if people know that the rules will only change if 67 Senators agree to change them, then the rules will never change. Realistically what I think is going to happen is that almost no significant legislation of any kind will pass until 2017, by which point the GOP will like control both the White House and the Senate and immediately eliminate the filibuster via the “nuclear” approach. Republicans, to their credit, tend to prioritize their vision of the national interests over issues of process and ego. Democrats, by contrast, seem to have mostly gotten into politics in order to bolster their own sense of self-righteousness and aren’t especially concerned with whether or not their conduct in office is efficacious.