For Senate reform advocates, tired of watching members come close to the "nuclear" line without crossing it, today is a pretty amazing day.
One way for this to happen would be for the presiding officer – most likely Vice President Biden or Senate president pro tempore Pat Leahy – to declare it unconstitutional, either in whole or in part (for example, for just judicial and executive nomination). That’s a break with Senate precedents, by which the body as a whole has to decide constitutional issues. A Republican Senator would likely appeal, and then a Democratic Senator would move to table the appeal, which would then go to a majority vote of the chamber. If a majority tables the appeal, the filibuster is effectively amended or ended. Alternately, a Democratic Senator could submit a point of order that the filibuster is unconstitutional (in whole or in part), after which the presiding officer would submit the question to the Senate as a whole. Usually, such a question would be subject to debate, but the presiding officer could break precedent and declare it undebatable. A Republican Senator would likely appeal, and then another Democratic Senator would motion to table that appeal, which would go to an immediate vote. If a majority votes to table, the Senate would proceed to vote on the original motion to declare the filibuster either wholly or partially unconstitutional. If a majority votes yes, the filibuster is amended or ended.