President Joe Biden called on Americans to band together to protect the right to vote and reject Republican-led efforts to change election laws, casting the battle as a globally watched test of U.S. democracy during an appearance Tuesday in Philadelphia.

“We’re facing the most significant test of our democracy since the Civil War,” Biden said in a roughly 25-minute speech at the National Constitution Center. “That’s not hyperbole — since the Civil War.”

He tied the fight directly to former President Donald Trump’s false attacks on the 2020 election, pointing to the numerous court cases, audits, and reviews that have upheld the result.

“The big lie is just that: a big lie,” Biden said. “You don’t call facts ‘fake’ and then try to bring down the American experiment just because you’re unhappy. That’s not statesmanship, that’s selfishness. That’s not democracy, that’s the denial of the right to vote. It suppresses. It subjugates.”

Biden, facing criticism from liberals that he hasn’t shown enough urgency on the issue, used his appearance to send out a high-stakes warning call to Americans.

But many of his supporters said words aren’t enough to meet the moment.

“Supporters of democracy will continue to organize and advocate, but we cannot organize our way out of this threat,” the Leadership Conference on Civil and Human Rights, an umbrella group of American civil rights groups, said in a statement.

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Democrats in recent weeks have seen their voting-rights bill stifled in the Senate and another Supreme Court decision further weaken the Voting Rights Act, while Republican state legislatures continue advancing laws that in many cases impose new voting restrictions in the name of election security.

Biden pointed directly to those laws, calling them a “21st-century Jim Crow assault.”

“They want to make it so hard and inconvenient that they hope people don’t vote at all,” he said.

Republicans immediately criticized Biden’s speech. Paris Dennard, a national spokesperson for the GOP, said the president was “stoking fear” and disputed that measures like requiring ID to vote disenfranchise voters.

Several liberal groups urged Biden to embrace calls to scrap the Senate filibuster, the rule that requires 60 votes for most legislation and has left Democrats unable to pass a federal voting-rights bill.

Biden didn’t mention the filibuster, instead calling for renewed efforts to pass Democrats’ sweeping voting-rights bill, the For the People Act. He repeatedly said U.S. allies are watching the political fight for signs of the health of the world’s leading democracy.

But he offered few hints of how Democrats’ bill could pass, indicating the limits of his powers and how far he is willing to push.

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With Democrats lacking the votes to end the filibuster, and Biden opposed to the idea anyway, he signaled that it could require a major electoral win next year to achieve his voting goals — laying the issue down as a defining topic in the midterm elections.

Republicans say Democrats are trying to impose national standards on elections and tilt the rules in their own favor. They point to polls showing significant support for voter ID laws and say Democrats are exaggerating the nature of the new restrictions. Lawrence Tabas, chair of the Pennsylvania Republican Party, said Biden should apologize for dividing the nation with his remarks.

“The president said that he wants to protect the sacred constitutional right to vote,” Tabas said. “The fact is we absolutely all are for that. Every American should be. We want to make sure that there is safe, reliable voting.”

Sen. Pat Toomey (R., Pa.) called the Jim Crow comparison “offensive,” saying it “trivializes a dark period of actual systemic racism in parts of America.”

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Biden began speaking shortly after 2:45 p.m. to a crowd of about 300, with spectators peering over the upper balcony and stairs in the Grand Hall of the museum.

Supporters at the event, including Democratic members of Pennsylvania’s congressional delegation, the Rev. Al Sharpton, and voting-rights advocates such as Paulette Whitfield of Strawberry Mansion cheered throughout the speech.

Whitfield, 68, said she appreciates Biden focusing a speech on voting rights, but is eager to hear what he’ll do: “It’s time for you to tell us what you’ll do about all this. What will you do for us?”

“All the speeches in the world will not matter if the filibuster does not end,” Bishop Dwayne Royster, executive director of POWER, a social advocacy group, said after Biden’s remarks. “We need real action, and we need it right now.”

Voting rights and Republican calls for tighter laws have roiled Pennsylvania ever since the lead-up to the 2020 election.

Republicans, often spurred by a litany of false claims about fraud, argue elections are too vulnerable and have challenged Democrats to identify specific voters who would be disenfranchised by their proposals. Independent research has long made clear that voter fraud is infinitesimally rare. So has every serious review of the 2020 results.

Biden arrived in Philadelphia days after State Sen. Doug Mastriano (R., Franklin), a likely gubernatorial candidate and a leading election denier in the state, moved to launch his own review of the 2020 election, targeting the city and two other counties.

“Philadelphia was a cesspool of corruption, which will soon be revealed by the audit,” Trump said in a statement Tuesday, despite a lack of any evidence of significant fraud in the city or elsewhere, including in the many lawsuits Trump filed.

Trump’s margins actually improved in Philadelphia compared to 2016.

Pennsylvania already conducted an audit of a sample of ballots in 63 of its 67 counties, which affirmed the accuracy of the outcome. Counties are also required by law to audit a small sample of ballots.

Gov. Tom Wolf, a Democrat, vetoed a sweeping election overhaul last month that would have tightened voter ID requirements, created early voting, and instituted new rules for drop boxes, among other major changes.

And around the country, Republicans have pushed to scale back voting access and take power away from local elections officials or punish them for mistakes.

In Texas on Monday, Democratic lawmakers left the state to deny Republicans a quorum and block voting on controversial GOP legislation that would ban drive-through and 24-hour voting and make mail voting more difficult.

In Georgia, the governor signed a measure giving lawmakers more control of the state elections board. Iowa increased the oversight its elected secretary of state has over county officials.

Biden said in his speech that some Americans don’t realize changes to voting laws aren’t just affecting how people vote, but who certifies those votes.

A Supreme Court ruling earlier this month intensified the debate by upholding an Arizona ban on counting absentee ballots delivered by anyone other than a relative. The court also upheld a requirement to dispose of any ballots cast in the wrong precinct. A lower court had ruled the regulations had an unequal impact on minority voters.

Timothy Jones, 41, drove in from Pittsburgh for Biden’s speech. Jones, a Navy veteran who has a felony record, moved from Florida to Pennsylvania in part because he wanted to be able to vote.

”We need a plan to counteract the attack on voting,” Jones said. “We need a message of hope and a message of healing because there are so many voters who are scared right now.”

Staff writer Laura McCrystal contributed to this article.