James Stewart is shown in a scene from the 1939 film “Mr. Smith Goes to Washington.” (AP)

When the 113th Congress convenes in January, one of the first things the Senate Democratic majority is expected to do is act to reform the filibuster. As my colleague Greg Sargent has noted, 50 senators are now on record supporting filibuster reform, and given that the caucus also believes that Senate rules can be changed through a simple majority vote at the start of a congressional session, this suggests strongly that changes will pass.

Then again, "filibuster reform" is a bit of a catch-all term. So what actually is on the table? Ryan Grim at the Huffington Post reports that Democrats are coalescing around a proposal by Sen. Jeff Merkley (D-Ore.). Under that plan, bills that fail to get a majority would fail immediately, but if a bill gets between 51 and 60, it will be debated as long as a senator is on the floor speaking about it. Once debate ends, a new vote would be conducted, and the bill could pass with a simple majority.

The idea is to return the filibuster to its origins, when senators held the floor and talked ad infinitum to prevent a bill from preceding, à la Mr. Smith Goes to Washington, or the 1964 filibuster of the Civil Rights Act by Robert Byrd and Strom Thrumond. But would that actually convert the Senate to a majority rules institutions from its current state, when a supermajority is needed to do anything of significance?

Filibuster experts aren't so sure. Sarah Binder, a political scientist and expert on congressional procedure at George Washington University, tells me that while the change may make it harder for individual senators to block bills, it won't prevent a united minority from keeping a bill from passage. "I suspect that in a war of wills between the parties, an intense minority might prevail," Binder writes. "After all, the majority typically has a full agenda on its plate and is just as likely to want to move on to other issues [giving in to the filibuster] as it is to battle it out with the minority." That means big bills that draw intense opposition, like the Affordable Care Act, might still need 60 votes.

Gregory Koger, a political scientist at the University of Miami and author of Filibustering, a history of the practice, agrees. "I would guess that this reform would most benefit major bills that the minority party is willing to block covertly but not overtly," he explains, citing Dodd-Frank as a prime example. Since obstruction would be more visible, it would be saved for major legislation, benefiting more mundane bills and nominations.

Both Binder and Koger emphasize, however, that a lot rides on the specific form the Merkley plan takes. Koger, for instance, notes that if unlimited amendments are allowed during the debate period, that could clog up the Senate just as much. So too could speeches, if the senators aren't forced to talk about the bill under consideration. "Does post-cloture vote debate have to be germane?" he asks. "Let's say the bill in question is immigration reform; can a filibustering senator give a 12-hour speech on U.S. policy in Afghanistan? Or the Petraeus affair?"

Binder thinks the reform would work best if paired with the elimination of the filibuster on "motions to proceed," which is the motion used to bring a bill to the floor for consideration. When the Senate majority leader want to debate and vote on a bill, currently he must motion to proceed, a motion which opponents currently can subject to a filibuster. Those kind of filibusters both slow down bills and prevent them from being debated.

"Knowing that it would be harder to derail a bill on the floor, the minority party would have little incentive to vote for cloture on the motion to proceed and little incentive to agree to a unanimous consent agreement to bring a bill to the floor and debate it," Binder explains.

This is why some political scientists, like Jonathan Bernstein, regard the "Mr. Smith question" as a bit of a distraction. The real question isn't whether or not blocking a bill requires extremely long speeches. It's whether blocking a bill is easy for the minority party.