It’s simple math. Lautenberg’s passing means Dems now only have 54 votes in the Senate. (His temporary Republican replacement can’t be expected to back rules reform.) Aides who are tracking the vote count tell me that Senator Carl Levin (a leading opponent of the “nuke option” when it was ruled out at the beginning of the year, leading to the watered down bipartisan filibuster reform compromise) is all but certain to oppose any rules change by simple majority. Senators Patrick Leahy and Mark Pryor remain question marks. And Senator Jack Reed is a Maybe.
If Dems lose those four votes, that would bring them down to 50. And, aides note, that would mean Biden’s tie-breaking vote would be required to get back up to the 51 required for a simple Senate majority. That’s an awfully thin margin for error.
On the other hand, Leahy, Pryor and Reed could be persuadable, or even already persuaded and keeping mum. Just four undecideds, even with Levin's opposition, means Republicans have some serious thinking to do about how far they're going to push opposition to Obama's three executive nominations that are still pending floor action, and three judicial nominations that haven't gone to committee yet. The commitment of the White House to back Reid on rules change, which presumably includes Biden's tie-breaking vote, adds one more component to everyone's calculations—the Republicans' willingness to keep obstructing and the Democrats' desire to do something about it.
The most effective course of action for us in the next month is to keep pushing Democratic senators to just do it.