It’s been called a “Jim Crow relic” by former president Obama, and Mitch McConnell threatened to launch a “nuclear winter” if the Senate attempts to end it. Increasingly, Democrats want to end it completely. So what is it, and why does it matter so much?

What Is the Filibuster?

The filibuster is a political strategy used by the Senate to delay, and often kill, votes on bills. Traditionally, a filibuster would mean that the resisting senator would stand on the floor and speak, sometimes for days, against a certain legislative effort.

When a senator utilizes the filibuster, they can delay a vote as long as they wish to — unless three-fifths of senators, currently 60 out of 100, vote to move forward.

Nowadays, senators aren’t even required to speak in order to deploy this tactic—they can essentially sign a note and curtail almost any legislation using the filibuster. (There’s also currently an exception to this rule called budget reconciliation that fast-tracks bills related to the federal budget and only related to the federal budget).

The Constitution does not include a filibuster. Instead, our founding document states that bills should only require simple majorities to pass, not supermajorities. Exceptions to this are impeachment charges, the expulsion of members of Congress, overriding presidential vetoes, and creating constitutional amendments.

The Founding Fathers were very clear: They did not want a minority party to be able to dictate what should be majority rule —and were fearful of this outcome.

In its first iteration, the U.S. Senate reconciled debates by voting on whether to end debates, thus moving a bill to an actual vote.

This changed when in 1806, Vice President Aaron Burr argued that this process of voting on whether to vote (called the previous-question motion) was redundant, as it was rarely ever used, and so it was ended. Inadvertently, Burr created a loophole that made it theoretically possible for senators to infinitely delay votes — and hence, we have the glacially slow, perpetually blocked governmental body that we know today.

What Has the Filibuster Been Used for, and How Has It Evolved?

One thing that stands out about the filibuster: It has consistently been used to curtail the rights of Black Americans.

Once rarely used in policy decisions, the filibuster only came into frequent use during the Civil War era, when Southern states would often deploy it in defense of slavery and while blocking anti-slavery legislation.

John C. Calhoun, sometimes referred to as the “grandfather of the confederacy,” was an important figure in developing the modern, common filibuster. “He did it for the express purpose of increasing the power of the slaveholding class,” says Adam Jentleson, whose book Kill Switch details the rise of the modern Senate. “What he saw at this time — this was around the 1830s and 1840s — was that slaveholders and slave states were becoming steadily outpowered in Congress. And so, he knew that if majority rule was allowed to continue, slavery was going to end.”

The filibuster was a solution to this issue and one of the reasons why the government remained incapable of simply ending slavery through democracy.

The filibuster was used throughout the 1800s and 1900s, with politicians challenging its legitimacy to various degrees without success. Woodrow Wilson edited it during WWI, after the Senate used it to stop him from arming ships against German U-Boats. With the help of public outcry, Wilson established Rule 22, which allows a two-thirds majority vote to invoke “cloture” — a rule that, essentially, limits filibustering to 30 hours.

From then on, the filibuster remained the same, though in 1975 the number of votes needed for a supermajority was changed to 60. Because earning a 60-vote majority is still quite difficult, the filibuster has remained an effective way for minority rule to block legislation.

Even after the Civil War, the filibuster was used to codify racial violence; for example, in 1922, the filibuster was used to defeat the Dyer Anti-Lynching Bill. Famously, the filibuster was also used to block civil rights legislation up until 1964. In protest of the Civil Rights Act, lawmakers filibustered for 57 days, until public pressure rose high enough for a supermajority to invoke cloture. Eventually, the supermajority necessary for cloture was changed to 60; but yet again, the filibuster remained firmly in place.

Since then, the filibuster has been used for various purposes on all sides of the political spectrum. It was the reason why George W. Bush couldn’t overhaul immigration legislation and why Barack Obama couldn’t pass climate legislation (or all that much of anything). It is the reason why bills still go to the Senate to die.

What Would Happen if the Filibuster Ended?

Without the filibuster, the Senate would be much more volatile than it is today. It’s possible that massive amounts of legislation could pass — and then be reversed, should the Senate majority’s political leanings change.

But Democrats have good reason to end the filibuster now (which is probably why Mitch McConnell is so scared). At the moment, Democrats want to enact a piece of voting rights legislation called the For the People Act. Among other things, the act would increase access to absentee voting, extend early voting, allow for same-day registration, and generally make it easier for people to vote.

“In the wake of an unprecedented assault on our democracy, a never before seen effort to ignore, undermine, and undo the will of the people, and a newly aggressive attack on voting rights taking place right now all across the country, this landmark legislation is urgently needed to protect the right to vote and the integrity of our elections, and to repair and strengthen American democracy,” the White House said in a statement.

Naturally, most Republicans hate the For the People Act as much as they hate the idea of getting rid of the filibuster. Their looming fear: The Democrat’s proposed voting rights reforms could make it much easier for Democrats to hold onto power. As of now, the bill passed in the House but of course has no chance of passing in the Senate, thanks to the filibuster.

Without the filibuster, Democrats would also have a shot at passing significant voting rights reforms, climate legislation, stricter gun control laws, and immigration reforms. They would be able to achieve their goals of fighting student debt, taxing the super-wealthy, making healthcare more affordable, and more.

Of course, the Democrats have an extremely slim majority in the Senate, and many Democratic senators are more centrist than progressive (see: Joe Manchin), meaning that achieving these goals would still require a serious fight even if the filibuster ended.

How Could the Senate End the Filibuster?

There are two ways the Senate could end the filibuster. 60 out of 100 senators could vote to end it, which will never happen in our current version of reality.

Or, senators could use a complex series of political moves sometimes referred to as the “nuclear option,” which involves three steps: First, a senator objects to a cloture ruling. Then the presiding officer rules this objection out of order, and a simple majority of senators could then vote to overturn that ruling, thus “blowing up” traditional Senate policies.

This “nuclear option” has already been utilized across party lines. Democrats used it to confirm some of Barack Obama’s nominees, and Republicans—led by Mitch McConnell—used it to confirm Donald Trump’s Supreme Court nominees. (Yes, McConnell, now the world’s biggest filibuster proponent, paused it so he could ram Supreme Court nominees through the system).

Ending the filibuster is a long shot, but Democrats know this may be their only chance to pass any significant social and political reforms. For his part, Joe Biden has not advocated for the end of the filibuster, but rather he supports the reinstitution of the “talking filibuster” — the “good old days” version of the filibuster where senators have to stand up and talk in order to obstruct the passage of a bill.

“It’s getting to the point where, you know, democracy is having a hard time functioning,” Biden told ABC.

Democratic senators Joe Manchin and Kyrsten Sinema also said they would not vote to end the filibuster, though Manchin did say he supports making it “more difficult to use,” which many centrist-leaning Democrats see as a promising option.

Still, despite the odds, those who support ending the filibuster see it as a life-or-death issue, as it’s quite possibly the only way to make true progress on inequality, gun control, healthcare, and other issues.

Currently, it seems that the Senate is hurtling towards a high-stakes battle for the future of the filibuster, with both sides ramping up their efforts to intimidate each other. McConnell’s threats to initiate a “scorched-earth Senate” if the filibuster is abolished has only encouraged those who want to end the filibuster, as it’s clear he’s genuinely afraid and believes there is a chance it could end.

Senate Majority Leader Chuck Schumer has been repeating the phrase, “Everything is on the table” in response to questions about the fate of the tactic. Indeed, everything is on the table, including the state of our present and future. The question is whether or not we can learn from the past.