The filibuster’s days are numbered. When it’s finally reformed (and it will almost certainly be reformed, not eliminated), the Senate will not become a paradise of wise legislating and democratic accountability. But it will be a much more responsive and effective place than it is now, and the momentum to get from here to there may be unstoppable.

For some time, it was only liberal Democrats in the Senate who wanted to see it go, so that bills with majority support could actually pass. But now moderates are becoming convinced — by the power of the arguments they’re hearing, the reality of Republican obstruction, and the tantalizing possibility that they might actually get to do the job they got elected for.

But each has their own reasons. In The Post on Wednesday, Sen. Angus King of Maine — an independent who caucuses with the Democrats — explained why he has changed his mind.

When King got to the Senate, he wrote, he was persuaded by the “what goes around, comes around” argument. If Democrats eliminated the filibuster to pass their own priorities, goes this line, then Republicans would be free to do the same the next time they took power, and the result would be a lot of policymaking Democrats didn’t like.

But now, King says, he is fed up:

But this argument is sustainable only if the extraordinary power of the 60-vote threshold is used sparingly on major issues or is used in a good-faith effort to leverage concessions rather than to simply obstruct. If, however, the minority hangs together and regularly uses this power to block any and all initiatives of the majority (and their president), supporting the continuation of the rule becomes harder and harder to justify, regardless of the long-term consequences.

This is significant, because King isn’t looking to get rid of the filibuster so Medicare-for-all or a universal basic income can pass. He’s one of the moderates — according to the widely respected Voteview ideological rankings, among Democratic senators only Kyrsten Sinema (D-Ariz.) and Joe Manchin III (D-W.Va.) are to King’s right.

As it happens, I and many others disagree with the logic of the “what goes around, comes around” argument that King still finds somewhat persuasive, also sometimes called “be careful what you wish for.” The terrible scenario its advocates posit — that your party gets to enact the agenda it advocates, and if the other party is elected, then they get to enact their agenda — is also known as democracy. It’s what an accountable system is supposed to look like; otherwise, the voters never get what they vote for.

It also reflects a terrible philosophy of governing, one that says I don’t mind if I achieve none of the policy changes I want, so long as the other party doesn’t, either. It makes gridlock the goal of the system, which inevitably makes voters disillusioned. And finally, it hurts Democrats much more than Republicans, because Democrats have a much more activist agenda for government action.

But if King still finds it somewhat persuasive, that’s okay. What he seems to envision is a system where the minority still has the power to obstruct — but only if it uses that power with restraint.

That was the situation for decades, when the filibuster required those who wielded it to hold the floor; it was used mostly to prevent Congress from passing civil rights laws. But today, the parties’ ideological sorting (there are almost no liberal Republicans or conservative Democrats left), and changes in the rules that allow the minority to create a filibuster literally by sending an email, have created every incentive for that minority to filibuster just about everything the majority wants to do.

So even senators like King have lost their patience. But this debate isn’t settled yet.

Former filibuster defenders, including President Biden and senators such as Dianne Feinstein (D-Calif.), are steadily inching their way toward reform, saying they’d be open to changes in the rule if Republicans continue to use it promiscuously. Each of them might have their own last straw in mind, the bill they will not tolerate being killed by the minority.

King, for his part, cites voting rights, writing that “if forced to choose between a Senate rule and democracy itself, I know where I will come down.” But for Biden, it might be infrastructure or workers’ rights or something else.

And we can be sure that the last two to agree to reform will be Manchin and Sinema, who have been most emphatic in their defense of the filibuster. Which, from the perspective of their own political interests and incentives, makes perfect sense, since they’ve constructed their identity as the Democrats who restrain other Democrats.

So when they finally come around, they’ll need two things. First, filibuster reform will have to be undertaken to achieve passage of a bill that is widely popular with their constituents, even many of the Republicans. Then they can say that the substantive matter at hand is so vital that they had no choice but to retreat on the filibuster.

Second, they’ll have to be the ones dictating the terms of the reform, and it will have to stop well short of simply eliminating the filibuster. Perhaps it will involve forcing the minority to talk, or adopting one of the other ideas to change it, but they’ll need to say because of their efforts, the filibuster still exists to protect the minority but it will no longer grind the chamber to a halt.

That’s the way this ends, and a new era where the party elected by the voters can pass the agenda those voters agreed to can begin. We’re not quite there yet, but the momentum is getting stronger by the day.

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