President Biden this week forcefully condemned a wave of voting restrictions proposed in Republican-led states and called on Congress to pass federal legislation addressing the issue.

Speaking at the National Constitution Center in Philadelphia, Biden said the spate of state-based election reform proposals is “the most significant test of our democracy since the Civil War.”

“This is a test of our time,” he said. “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.”

Biden and Democratic lawmakers are increasingly frustrated with their inability to move one of their top legislative priorities, the For the People Act (S. 1), in the Senate. The bill passed the House in March on a party-line vote but Senate Republicans have no intention of supporting it. Key provisions of the bill include expanding automatic voter registration and same-day registration; strengthening voting by mail, early voting and ballot access; combating voter intimidation and suppression; protecting elections from foreign interference; fixing partisan redistricting; and forcing disclosure of “dark money” donations to political groups. Senate Minority Leader Mitch McConnell (R-KY) has accused Democrats of trying to “rewrite the rules of our system.”

“Our democracy is not in crisis,” he said last month, “and we are not going to let one party take over our democracy under the false pretense of saving it.”

Biden and congressional Democrats say the bill is needed to combat voting bills in a number of states that would make it harder for communities of color to vote. Democrats in Texas fled the state Monday to deny Republicans the quorum needed to pass new voting laws in Texas. Many of them flew to Washington and met with Senate Majority Leader Chuck Schumer (D-NY) and Vice President Kamala Harris.

While Biden’s speech this week was forceful, the president stopped short of endorsing changes to the filibuster that would enable Senate Democrats to pass the federal voting rights bill. Biden is under increasing pressure from Democratic lawmakers and civil rights leaders to endorse a more aggressive tactic.

White House press secretary Jen Psaki said it’s up to Senate leaders to change the filibuster, not the president.

“A determination about making changes will be made by members of the Senate, not by this president or any president, frankly, moving forward,” Psaki said. “If it were waving a magic wand to get voting rights legislation on his desk through any means, he would do that. But it requires the majority of members in the Senate to support changes to the filibuster.”