(J. Scott Applewhite/AP)

Proponents of overhauling the curious Senate custom see a window of opportunity, but it’s a narrow one with plenty of chances to cloud up.

After opposing filibuster reform, Senate Majority Leader Harry Reid (D-Nev.) is now in favor of tweaking it, blaming the procedure for tying the closely divided Senate in knots.

If there’s going to be any action, it’s likely to come in the first day or so of the new session. The crux of the argument for taking what’s known in Senate parlance as the “constitutional option” (in which the Senate rules would be changed with the consent of only a simple majority) is that the Senate’s rules don’t carry over from session to session, and so making a change would have to happen in the early hours of the new Congress.

Another unknown is that even reform-minded Senators aren’t sure just how far Reid is willing to go. He’s said he’s for the idea of eliminating the use of the filibuster on “motions to proceed,” which essentially allow individual senators to block bills from ever coming up for debate. But Reid’s been coy about what other changes he’d embrace.

And unrelated bipartisan negotiations over the “fiscal cliff” could make it dicier for Reid to jump off the institutional cliff by forcing the issue — after all, if he’s working a deal with Republicans, it will be harder for him to roil the waters by making a controversial move on the filibuster.

In an alternate scenario, the chances are far murkier. If Republicans wrest control of the Senate and GOP Leader Mitch McConnell (R-Ky.) is in the driver’s seat, he could face pressure from some Republicans within his caucus to rein in the filibuster (after all, it’s a minority’s best friend) — particularly if there’s a Republican president in the White House.

GOP candidate Mitt Romney loves to talk about repealing Obamacare on day one of his presidency, and that won’t be possible with the filibuster in place, as is.

But McConnell doesn’t support filibuster reform -- even with a GOP majority in the Senate -- believing instead that the chamber can function more smoothly without a rule change. “This is not about the rules,” he said on the Senate floor last month. “The rules have remained largely the same over the years. This is about us. And this problem can be fixed. All we have to do is decide to operate differently.”

And what are the chances of that happening?

So far, discussions about the course of action have been under the radar, with most senators taking a wait-and-see approach until after Nov. 6.

But Richard Arenberg, a former Senate staffer and co-author of “Defending the Filibuster: Soul of the Senate” says that the best course to take would have been changing the rules through the traditional process -- by a super-majority of at least 67 votes. Arenberg said that, with neither side sure who was going to hold the majority, the last few weeks of September before recess could have been a golden hour for bipartisan negotiations, leading to reforms that would have been the Senate more functional. “At that point, the only question on the table would have been ‘what’s best for the Senate?’” he said.