Senate Majority Leader Chuck Schumer (D-N.Y.) announced in a letter to his colleagues this week that the chamber would vote by Jan. 17 on whether to change the Senate rules if Republicans filibuster voting rights legislation in the coming days. 

To pass voting rights legislation—something Democrats see as crucial to their success in the 2022 midterm elections—they would need to first remove or weaken the filibuster, which Republicans have used to stymie much of their legislative agenda. In his letter, Schumer specifically linked Jan. 6—the day that Trump supporters stormed the U.S. Capitol, fueled by the former president’s false claims of a “rigged election”—to the Democrats’ voting rights legislation. 

“Make no mistake about it: This week Senate Democrats will make clear that what happened on January 6th and the one-sided, partisan actions being taken by Republican-led state legislatures across the country are directly linked,” Schumer wrote. “We hope our Republican colleagues change course and work with us. But if they do not, the Senate will debate and consider changes to Senate rules on or before January 17, Martin Luther King Jr. Day, to protect the foundation of our democracy: free and fair elections.”

President Donald Trump’s claims of election fraud are false. But they have spurred efforts by Republican state legislatures in places like Georgia, Iowa, Florida, and Texas to pass new laws restricting voting. Restrictive voting measures typically have an outsize effect on voters of color, a (broad) group that tends to vote Democrat. That’s why it is imperative, Democrats argue, that Congress passes voting rights legislation now, before they risk losing their narrow majorities in both the House and the Senate in this year’s midterm elections.

“Democrats perceive the issue of voting rights as sort of a do-or-die issue,” said David Schultz, a political science professor at Hamline University. “If they can’t guarantee that their base and people likely to support Democrats can vote, they’ve lost everything.”

Democrats hope to pass two bills: the Freedom to Vote Act, and the John Lewis Voting Rights Advancement Act. The former would make Election Day a public holiday, expand the types of identification allowed at the polls (to include things like federal or state-issued IDs, military or veteran IDs, and tribal IDs), and mandate 15 days of early voting for federal elections. The latter bill would restore and strengthen parts of the Voting Rights Act of 1965, such as the return of “preclearance,” which requires that states with a history of racist voting practices submit any election rules for federal approval.

“As state legislators come back into session, many of the 400-plus voter suppression bills that have been introduced last year get carried over to this year,” said Aaron Scherb, legislative affairs director at Common Cause, a left-leaning government watchdog group. “There’s an urgent need to protect the voices of Americans—especially Black and brown Americans, whose voices many of these laws are targeting.”

Republicans have opposed the two bills, arguing they extend too much power to the federal government. “This is not a federal issue. It ought to be left to the states,” Senate Minority Leader Mitch McConnell (R-Ky.) said at a press conference last year. “There’s nothing broken around the country.”

Because there is a 60-vote threshold in order to clear the filibuster, Democrats need 10 Republicans to join them in order to advance the legislation—a near-impossible task. 

Assuming Democrats can’t get the 60 votes needed to overcome a filibuster, their only path forward lies in filibuster reform. And that’s unlikely to get the support of senators Joe Manchin (D-W.Va.) and Kyrsten Sinema (D-Ariz.), both of whom remain publicly unwilling to change the filibuster rules.

“Democrats at this point seem likely to lose control of the House, Senate, or both after the 2022 elections, and so this may be their last opportunity for a while to try to pass such legislation, which divides the parties deeply,” Rick Hasen, a law professor at UC Irvine, told Fortune. “The only way this passes is if senators Manchin and Sinema are willing to go for some kind of filibuster change. There’s no margin for error.”

In the (almost-certain) event that Manchin and Sinema refuse to eliminate the filibuster, Democrats could still work with them on other reforms, like bringing back the talking filibuster, which would burden a senator in the minority to hold the floor with a speech, or nixing the ability to filibuster a bill before it’s even been debated on the Senate floor. 

“We’ve been here almost a year, and we’ve seen enough: It’s time to change the filibuster to protect voting rights,” Sen. John Hickenlooper (D-Colo.) said in a statement, referring to the amount of time that Democrats have held the majority in Congress. “Protecting the right to vote shouldn’t be a partisan issue, and we set out to work across the aisle. But three separate voting rights bills have failed in the Senate this year.”

Nearly 150 U.S. mayors would agree. The U.S. Conference of Mayors published a letter on Monday signed by 146 mayors (most of them Democrats), pushing the Senate to pass the Freedom to Vote Act and the John Lewis Voting Rights Advancement Act. 

“American democracy is stronger when all eligible voters participate in elections,” the letter reads. “Yet voting rights are under historic attack and our very democracy is threatened.”