On Aug. 6, 1965, President Lyndon B. Johnson signed the Voting Rights Act, finally making good on the U.S. Constitution’s promise that no citizen should be denied the right to vote.

The sweeping legislation outlawed discriminatory practices like bogus literacy tests that were used by some states to deny African Americans access to the polls, and gave the federal government the authority to stop states from passing new laws that would have the same effect. It had an immediate and sustained impact, enfranchising millions of men and women and bringing people of color into the highest levels of government. Its protections have been extended to other groups, extending the franchise to citizens who don’t speak English or who have disabilities.

This year, the anniversary comes around as the landmark law has been weakened by a pair of U.S. Supreme Court rulings and a modern update is stalled in Congress, unanimously blocked by Republicans in the Senate. Meanwhile, states such as Georgia and Texas are passing voter suppression laws that will not make it not only harder to vote, but also easier for state legislative majorities to throw out legitimate election results. Without federal action, these new laws will disproportionately hurt Black, Latino and poor voters.

This assault on voting rights is nothing new, but the history of the Voting Rights Act should make clear what’s at stake.

The passage of the 1965 law is one of the great achievements of the modern civil rights movement. It was made possible by decades of activism led by Dr. Martin Luther King Jr. and many others, which culminated in the 1965 march from Selma to Montgomery, Alabama. Nonviolent protesters were beaten for asserting a basic right of citizenship. Their sacrifice inspired the nation, and Johnson addressed a joint session of Congress with new urgency, saying the activists were fighting for the rights of all Americans.

“Their cause must be our cause, too,” Johnson said. “Because it is not just Negroes, but really it is all of us, who must overcome the crippling legacy of bigotry and injustice.”

He paused, then added: “And we shall overcome.”

The applause was thunderous, but not everyone was cheering. Most Southern Democrats in Congress wanted to maintain the system of racial exclusion and opposed the bill, blocking action on it in the Senate for 23 days with a filibuster.

Johnson, a Democrat, was able to work with Republicans like Senate Minority Leader Everett Dirksen, R-Ill., so that 23 out of 32 Republican senators, including Maine’s Margaret Chase Smith, voted to break the Southern filibuster, opening the way to the bill’s passage, 56 years ago this week.

The Act was seen as a bipartisan success at the time, but like many other issues, it’s become polarized.

In 2013, the conservative majority on the Supreme Court decided that racial discrimination is a thing of the past, and took away a requirement that jurisdictions would have to pre-clear any changes to voting practices, even if those districts had a history of discrimination. This year, the conservative justices ruled that theoretical voter fraud is a bigger threat to democracy than documented racial injustice, so states can institute anti-fraud measures, even if they disproportionately affect certain groups.

Bills that would have addressed these and other problems have passed the House, but unlike 1965, on a purely partisan basis. In the Senate, all 50 Republicans, including Maine Sen. Susan Collins, voted to filibuster the For the People Act, keeping it from coming forward for debate.

Senate Democrats are said to be working on a scaled-back version of the bill that could be presented as soon as this week. This version is said to include a minimum standard for early and mail-in voting, an end to partisan gerrymandering for drawing House districts and a requirement that “dark money” groups disclose their contributors.

The Voting Rights Act of 1965 could not have been possible without a bipartisan, multiracial coalition built around our shared values. It will not survive if Republicans treat voting rights as a political lever they can use to lower participation whenever high turnout is not to their advantage. This anniversary should remind us that the victories of the past are easily erased if we don’t keep trying to overcome the crippling legacy of injustice.