This story has been updated.

President Biden and congressional Democrats ran in 2020 on an ambitious agenda, including big promises on infrastructure, climate change, immigration and jobs. And after winning the House, the White House and, by the slimmest of margins, the Senate, Democrats saw the rare opening to pass transformative legislation.

Biden got off to a quick start on coronavirus relief, and Democrats were able to get their bill through the House and the Senate using a procedural maneuver called reconciliation. It’s a special set of rules that can only be used to pass funding and tax measures.

For everything else, there’s a big hurdle in the way of Democrats’ legislative priorities: The filibuster.

The question of what to do about the filibuster — whether to leave it intact, modify it or get rid of it completely — is an intense one that has probably been sidelined as of this week. Any change would require the votes of all 50 Democrats in the Senate, and one of them, Sen. Joe Manchin III of West Virginia, said in April that “there is no circumstance” in which he’d vote to change or eliminate it.

That statement, in an op-ed Manchin wrote in The Washington Post, was about as purposefully unequivocal as it gets for a politician. It wasn’t out of line with his previous statements, but it seems to slam the door for now on Democrats’ hopes of moving on the items that Republicans won’t go for — which are most of their priorities.

Because of that, we’re likely to still hear a lot about the filibuster. So let’s explore exactly why it’s the most important rule in politics right now.

What is the filibuster?

The filibuster is a Senate rule that essentially requires 60 votes to pass most legislation (for example, the measures Democrats can’t get through using reconciliation, like a minimum-wage increase or immigration reform).

The Senate is required to follow certain procedural steps in passing legislation. When a bill is brought to the Senate floor, any senator can bring things to a halt by speaking for as long as they wish, effectively delaying a vote to end debate on a bill. The Senate can vote to end debate by invoking cloture — another procedural step — with a three-fifths majority, or 60 of 100 senators. So any bill that has the support of at least 60 senators is, in effect, filibuster-proof, and the Senate can quickly move on to the next steps leading up to a final vote. But without 60 senators (remember, Democrats only have 50 right now), the filibuster cannot be broken.

In the modern Senate, an objecting senator doesn’t actually have to stand there and filibuster endlessly — you might remember Sen. Ted Cruz (R-Tex.) reading “Green Eggs and Ham,” or Sen. Marco Rubio (R-Fla.) quoting Jay-Z and Wiz Khalifa, in the midst of hours-long speeches that brought the Senate to a standstill. Those moments weren’t technically filibusters, because the “talking filibuster” was eliminated decades ago. They were more temporary delay tactics, with cloture votes taking place soon afterward. But they give a good sense of what talking filibusters were like — typifying the long, seemingly pointless speeches that characterized senators’ attempts to delay legislation in the talking-filibuster era.

So now, a senator can simply indicate his intent to filibuster a bill and cause it to be sidelined. That means, in the current Senate, all it takes is one Republican to object to a Democratic-sponsored bill and that bill is stopped in its tracks before ever getting to a final floor vote.

Democrats are facing renewed pressure to end or change the legislative filibuster, but The Fix’s Aaron Blake explains why that’s unlikely. (JM Rieger/The Washington Post)

How the filibuster has changed in recent years

Legislation is the last big area of Senate business to which the filibuster applies. It used to apply to judicial nominations, but Democrats voted to eliminate the filibuster for judicial nominations except for Supreme Court justices in 2013, and Republicans followed up by eliminating the filibuster for Supreme Court justices in 2017.

Democrats made that first big change in 2013 after Republicans held up the nominations of dozens of Obama administration officials that needed Senate confirmation, as well as nominees for federal judgeships. Getting rid of the filibuster for those nominees was seen as a huge departure from Senate tradition — but Democrats paid for it once Republicans took back the Senate a year later, then won the presidency in 2016. That set up then-Senate Majority Leader Mitch McConnell (R-Ky.) to confirm hundreds of federal judges during the Trump years, without needing 60 votes. And in 2017, eliminating the filibuster for Supreme Court nominees enabled the GOP to put three conservative justices on the court, after refusing to consider Obama nominee Merrick Garland.

President Trump's remaking of the federal judiciary follows a three-decade period of rising partisanship — and hypocrisy — over federal judicial nominees. (JM Rieger/The Washington Post)

That’s put the Senate on a trajectory toward slowly returning to majority rule, and the last big hurdle is legislation. Democrats have been considering eliminating the legislative filibuster since well before they won back the Senate in January — including during the 2020 election — and it’s a discussion that is getting louder as they get closer to moving beyond the kind of bills they can pass through reconciliation.

The case for changing it now

Democrats who want to change the filibuster caution that they might have a limited window to pass the legislation they want ahead of the 2022 midterm elections. Midterms are scary for the party in power. Traditionally, midterm elections lead to losses in Congress for the party holding the White House. If Democrats lose either the House or the Senate in 2022, passing big-ticket legislation during Biden’s first term is essentially off the table.

So, they say, why not use every tool available to pass new laws now? They have the majority and the procedural power to do it. And, proponents argue, it’s a lot harder to undo existing legislation once it’s already in place (see: the Affordable Care Act).

Democrats also seem to expect little in the way of bipartisan cooperation — or even real negotiations — on big-ticket bills.

And in the one area they have had real negotiations – infrastructure – Democrats want to pass a separate reconciliation bill to fund the priorities Republicans refused to include in a scaled-back bipartisan bill Biden said he and a bipartisan group of senators agreed to on June 24.

The case for keeping it the same

There are a few cases for keeping the filibuster as it is now. Manchin, in signaling he won’t vote to change it even if the rest of his Democratic colleagues do, says it’s about forcing the kind of bipartisan cooperation that has become rare in the Senate.

“The time has come to end these political games,” Manchin said on Wednesday, criticizing the kind of partisan procedural maneuvering that has become the norm in the Senate, “and to usher a new era of bipartisanship where we find common ground on the major policy debates facing our nation.”

McConnell, now the minority leader, made a similar argument in March.

“The framers designed the Senate to require deliberation, to force cooperation and to ensure that federal laws in our big, diverse country earn broad enough buy-in to receive the lasting consent of the governed,” McConnell said.

There’s also the fact that Democrats probably won’t control the chamber forever — perhaps not even for the remainder of Biden’s term. Republicans having full power and no filibuster could result in all sorts of Democratic nightmares — abortion rights rollbacks chief among them. Groups such as Planned Parenthood are reportedly wary of changes that could hand Republicans the ability to enact national antiabortion policies the next time they win the White House and both chambers of Congress.

McConnell’s ability to confirm federal judges at will during the Trump administration was a real thorn in Democrats’ sides, and some regretted starting filibuster reform in 2013. McConnell has promised to bring the Senate to a complete standstill with procedural maneuvers if Democrats gut the filibuster.

“Nobody serving in this chamber can even begin to imagine what a completely scorched-earth Senate would look like,” McConnell said on March 16. “I want our colleagues to imagine a world where every single task … requires a physical quorum, which, by the way, the vice president does not count in determining a quorum.”

McConnell is basically saying that if Democrats gut the filibuster, Republicans will make the Senate unbearable. They’ll make it a pain to do things as simple as turning on the lights.

Proponents of changing the filibuster say that only serves to force Democrats to make concessions to Republicans who aren’t that interested in negotiating in the first place.

If nuking the filibuster is off the table, what smaller changes could be made?

After Manchin’s announcement — which left him little wiggle room to change his mind — filibuster reform seemed dead in the water. Manchin has carved out a space for himself as the most moderate Democrat in the Senate, occasionally infuriating those in his party who see him as stopping their agenda cold.

But it isn’t just Manchin — there isn’t even a cohesive plan from Democrats at this point.

To change the rules at all, Democrats would need all 50 Democratic senators onboard. And several have been vocal in opposing big changes beyond Manchin, including Sen. Kyrsten Sinema (D-Ariz.).

“When you have a place that’s broken and not working, and many would say that’s the Senate today, I don’t think the solution is to erode the rules,” Sinema told the Wall Street Journal. “I think the solution is for senators to change their behavior and begin to work together, which is what the country wants us to do.”

Some of Sinema’s Democratic colleagues say that’s wishful thinking, and that Republicans simply aren’t interested in changing.

“One hundred percent of our focus is on stopping this new administration,” Senate Minority Leader Mitch McConnell (R-Ky.) said in May. And that’s exactly how McConnell and Senate Republicans treated the Obama administration, too. As more of Democrats’ legislative priorities are stopped cold by GOP filibusters, patience is wearing thin. And some Democrats say that could lead senators to soften on at least changing the filibuster rules.

“I think as people see (Republicans) stopping more things, minds might change,” Sen. Amy Klobuchar (D-Minn.) told The New York Times.

Manchin’s position seemed to soften slightly in a zoom call with donors, in audio leaked to The Intercept on June 16.

On the call, Manchin suggested the onus should be on senators blocking a bill to explain their position on the Senate floor – something closer to the “talking filibuster” that used to exist in the Senate and the Biden has endorsed returning to.

Other Democrats want to go farther, though; Some want to lower the threshold for moving forward on legislation to 55 votes, instead of 60. There’s precedent for that: Decades ago, the threshold was 67 votes, until it was changed in the 1970s.

Sinema might be right that the public wants the Senate to function in a more amicable way. But achieving it will take a willingness to sit down and talk that has been absent from the Senate for a long time now. And highlighting that dynamic – and Republicans’ apparent desire to stop as much Democratic legislation as they can – might be the most effective tactic, for now, in trying to convince holdouts like Sinema and Manchin to change their minds.