Harry Reid's recent vow to reform the filibuster has cheered advocates for procedural reform. But there remains a question: Which reforms, exactly, would he support?

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On Wednesday, Reid singled out the abuse of a procedural step called the motion to proceed — a vote that's necessary for a bill to move to debate on the Senate floor. "I've made it all very clear in all of my public statements about the need to get rid of the motion to proceed," Reid said on the Senate floor, according to a preliminary transcript.

But even if this change were made, there would still be ample opportunities for minority to block a bill, says Sarah Binder, a political scientist at George Washington University. Eliminating the filibuster on the motion to proceed would make it easier for the majority to set the legislative agenda and bring bills to the floor for debate. But it wouldn't stop the minority from filibustering a bill's final passage. Rather than eliminate obstructionism, "it might shift it and put focus elsewhere," explains Binder.

That's why other reform advocates have proposed eliminating the filibuster altogether or having a scheduled phase out, as Sen. Tom Harkin (D-Iowa) proposed in 2010. Under Harkin's plan, my colleague Greg Sargent explained, the first vote to move final passage "would require 60 votes to break the filibuster, followed by motions requiring 57, 54, and finally, 51 votes" — i.e. a simple majority. That's why Sen. Sheldon Whitehouse recently advocated for targeting "the double filibuster, filibustering both the motion to proceed to the bill and then the bill itself." But these more drastic reforms are an even more difficult sell, politically speaking.

Reid's office didn't respond to questions about whether he'd support filibuster reforms that went beyond the motion to proceed, and he has yet to unveil specific proposals. But the Senate Majority Leader has apologized repeatedly for blocking the Harkin-Udall-Merkley bill that included a few other procedural reforms in addition to ending the motion to proceed filibuster: The legislation would eliminate secret holds, guarantee amendments offered by the majority and minority, require a "talking filibuster" in which senators actually had to hold the floor, and expedite nominations.

Congressional experts note there are a few other alternative reforms to consider. Binder suggests that the Senate could create more types of "fast track" legislation that only needs a simple majority to vote, as is already the case for budget reconciliation and ending a military operation through the War Powers Act. Alan Frumin, the former Senate parliamentarian, has suggested that the Senate should expedite certain nominees "essential to the staffing of the president’s administration" to reduce gridlock.

Filibuster reform advocates themselves are divided on the best approach to reforming the filibuster. Common Cause, for instance, believes the filibuster is not only unnecessary but also unconstitutional, having filed an unsuccessful lawsuit on those grounds. Others, like the Communication Workers of America, believe that it's better for some version of the filibuster should stay. But both want Reid and other legislators to go beyond simply tackling the filibuster on the motion to proceed. "We think that would be an important step, but we don't think that's far enough," says Shane Larson, CWA's legislative director.