PHILADELPHIA — President Biden on Tuesday delivered his most forceful condemnation yet of the wave of voting restrictions proposed in Republican-led states nationwide — efforts the president argued are the biggest threat to American democracy since the Civil War.

Biden’s speech was an attempt to inject new life into flagging efforts to pass federal legislation addressing the issue. But while he intensified his explanation of the stakes, his speech did not include a call for the Senate to change the filibuster, which is seen by advocates as the best, and perhaps only, way to usher in the kinds of changes Biden is seeking.

At the National Constitution Center in Philadelphia, in a room filled with images of Benjamin Franklin and quotes from Daniel Webster and Theodore Roosevelt, Biden compared the new laws to voter suppression by the Ku Klux Klan and to the Jim Crow-era laws that disenfranchised nearly all voters who were not White and male. He railed against laws that restrict access — calling them “raw and sustained election subversion” — and said that the 2022 midterm elections could highlight the damaging effects of the new laws.

“This is a test of our time,” he said to a crowd of 300 civil rights advocates, top advisers, and local officials.

“Hear me clearly,” he added. “There’s an unfolding assault taking place in America today, an attempt to suppress and subvert the right to vote and fair and free elections. An assault on democracy, an assault on liberty, an assault on who we are.”

He urged Americans to channel their concern into action.

“We’re facing the most significant test of our democracy since the Civil War,” he said. “That’s not hyperbole. Since the Civil War — the Confederates back then never breached the Capitol as insurrectionists did on January the 6th. I’m not saying this to alarm you. I’m saying this because you should be alarmed.”

Biden also mounted a robust defense of the election that led to his presidency, one that Trump and his allies have repeatedly and falsely said was conducted fraudulently.

“With recount after recount after recount, court case after court case, the 2020 election was the most scrutinized ever,” Biden said. “The ‘big lie’ is just that: a big lie!”

The remarks came amid a dramatic escalation around voting rights, with Democratic Texas legislators fleeing their home state Monday to deny Republicans the quorum needed to pass new voting restrictions. Most of the state’s House Democrats flew to Washington to plead with Congress to pass new federal voting laws. They met with Senate Majority Leader Charles E. Schumer (D-N.Y.) and Vice President Harris on Tuesday.

“I know what you have done comes with great sacrifice, both personal and political,” Harris told a group of lawmakers, comparing their actions to past moments in voting rights history. “Defending the right of the American people to vote is as American as apple pie.”

But there are major questions about any pathway forward for Democrats. Those in the Texas Legislature can only stay away from their state for so long. Biden has been reluctant to press for the changes to the filibuster that would be needed for his party to push through its legislative package. He didn’t bring up the filibuster at all in his Tuesday speech.

Biden did call for a “new coalition” of activists, students and leaders from the faith, labor and business communities to help bolster voter education and eventual turnout at the polls.

“We have to ask, are you on the side of truth or lies, fact or fiction, justice or injustice, democracy or autocracy?” he said. “That’s what it’s coming down to.”

The speech also comes as Biden faces escalating pressure from Democratic lawmakers and civil rights leaders to more forcefully use his bully pulpit on voting rights, particularly as legislative efforts on the issue collapsed on Capitol Hill last month.

Biden last week met with civil rights leaders at the White House for what the Rev. Al Sharpton described afterward as “a very candid, no-holds-barred meeting.”

“Last Thursday, when we met with him, we said we wanted him to use his bully pulpit,” Sharpton said. “He used it today.”

After the speech, Sharpton said he pulled Biden aside and urged him to drop his reluctance and start calling for changes to the filibuster.

“I said on the side to him, I’m still waiting on the filibuster. He said, ‘We’re still working through our position on that.’ So he’s noncommittal,” Sharpton said. “You’ve got to do a workaround or change the filibuster. Otherwise, all of what he said, and we’ve been saying, is at risk here.”

Republicans have accused Biden of misrepresenting their efforts to impose stricter voting laws.

“Joe Biden and Democrats have an election power grab playbook: lies and theatrics,” Danielle Alvarez, the Republican National Committee communications director, said in a statement. “After Democrats failed to pass their federal takeover of our elections (H. R. 1), Biden is continuing their dishonest attacks on common-sense election integrity efforts.”

In addition to Biden’s tasking of Harris to lead the issue, his Justice Department has sued the state of Georgia over voting restrictions signed into law earlier this year. But unanimous Republican opposition on federal legislation has blocked efforts in Congress this year to expand voting access and enact what Democrats call good-governance measures, and a handful of moderate Democratic senators have been resistant to blow up long-standing Senate rules that would allow voting legislation to more easily clear the chamber.

White House press secretary Jen Psaki said that Biden will “certainly continue” to discuss the issue of voting rights across the country, emphasizing that he believes that expanding these rights is the “fight of his presidency.” But she has also made clear that he has little intention to push for changes to the filibuster.

“Determination about making changes will be made by members of the Senate, not by this president or any president, frankly, moving forward,” she said Monday. And regarding a special exemption for voting rights, she said, “We don’t have any new position on that, either.”

While the president has no direct power over Senate rules — which get revised by a vote in the chamber — he has attracted criticism from members of his own party who believe Biden has not used the full powers of the presidency to force change in the gridlocked Capitol and are warning that failure to pass a pair of two key voting bills in Congress will be a stain on his legacy.

One of the more vocal critics — Rep. Mondaire Jones (D-N.Y.) — said he believes Biden should be doing more now to ensure the issue of voting rights is addressed this year before redistricting gets fully underway and ultimately, along with the loss of minority voters, prevents Democrats from possibly holding the majority over the next decade.

“It’s like everyone understands that the path for Republicans being in control of the federal government again is voter suppression except for the one person who has the influence to do something about it right now in this moment,” Jones said in an interview.

House Democrats have no sway over Senate rules except adding to the public pressure to change them. Still, House Majority Whip James E. Clyburn (D-S.C.) has not lost hope that the Senate will bend on the filibuster rule, going as far as to suggest that it’s possible they can create a special carveout for a new rule that could shepherd through the For the People Act and the John Lewis Act with only Democratic votes. The latter bill, named for the late civil rights icon, would reauthorize parts of the 1965 Voting Rights Act that were struck down by the Supreme Court.

 Clyburn said if someone like Sen. Robert C. Byrd (D-W.Va.) had the power to eliminate the filibuster rule on budgetary issues, he also can “envision a Manchin rule” in which someone like Sen. Joe Manchin III (D-W.Va.) can propose a similar carveout for legislation that directly deals with the Constitution or a one-time rule to allow both voting rights bills to easily pass.

After facing some heat for suggesting earlier this week that Biden should be more proactive in pressuring senators to support bending filibuster rules to protect voting rights, Clyburn clarified that he feels confident the president is doing enough to ensure something gets done soon.

“I think that people tend to feel that nothing has happened unless they hear it over a microphone. A lot can happen over the telephone. So I’m convinced that Joe Biden is committed to this and he’s working on these issues,” Clyburn said in an interview. “And just because he’s not standing in front of a microphone telling everybody what he’s doing, that doesn’t mean he’s not on the telephone doing a lot behind the scenes.”

But the dynamics have changed little in the Senate, where Democrats have been mostly unified behind elections and voting legislation but divided on whether to dismantle the filibuster to actually pass the measures. In the absence of legislation, senators are holding hearings and continuing to highlight the issue, while pushing the Biden administration — particularly the Justice Department — to do more to challenge voting restrictions they feel are unconstitutional.

“They’ve done a lot already with Georgia, and the question is whether they’ll do more,” Senate Judiciary Committee Chairman Richard J. Durbin (D-Ill.), referring to the Justice Department lawsuit. “I encourage them, where they have a case, work it.”