Lucy swiped that #$@#ing ball away from us again:

So Harry Reid and Mitch McConnell have reached a deal under which both have vowed never to pass any rules reforms via the "Constitutional option," which only requires a simple majority vote. The idea is that if one side rams through reforms this way, the other will retaliate when it gains the majority. Take this option off the table, and future reforms will only pass with bipartisan support.

Reportedly, Reid could not keep his caucus together, with several vulnerable senators worried that this would be used against them in ads by Republican challengers and fearful of retribution if they lost the majority in 2012, although Tom Udall (D-NM) did his damndest to keep filibuster reform on the table:

Udall's argument: If Democrats hadn't threatened to pass filibuster reforms via a simple majority, the issue would have been a non-starter from the very beginning. If the reforms being championed by Udall, Tom Harkin and Jeff Merkley could only pass with 67 votes, everyone could have safely ignored them and the issue would have received no attention.

As Udall put it, the current discussion wouldn't have happened at all "if we hadn't utilized our rights under the Constitution, if we hadn't pushed this very hard and said we are trying to round up 51 senators that will stand up with us and say we want
change in this institution."

By agreeing to take this option off the table, of course, Reid and McConnell have effectively ensured that this leverage won't be available in the future. As Ezra Klein explains, this ensures that "the minority is not on notice that further abuse of the filibuster (and associated stalling tactics) could lead to more significant reforms."

But hey, "secret holds" are no longer okay...sort of. Which means with no leverage and no teeth, the Senate will be exactly the same dysfunctional legislative body it was last year.