The bill would bring about the largest overhaul of U.S. elections in a generation, touching on almost every aspect of the electoral process. Democrats say the changes are even more important now as Republican-controlled states impose new voting restrictions after the divisive 2020 election.

Yet it’s a motivating issue for Republicans, too, with GOP Senate leader Mitch McConnell so determined to stop Democrats that he’s personally arguing against the measure, a rare role for a party leader that shows the extent to which Republicans are prepared to fight.

Republicans will offer scores of amendments to highlight aspects of the bill they believe are unpopular, including the creation of a public financing system for political campaigns, an overhaul of the federal agency that polices elections and dozens of provisions that would dictate how states conduct their elections.

“We should be finding ways to rebuild trust, not destroy it further,” McConnell told the Senate Rules Committee, pointing to the bitterly contested outcomes of the past two presidential elections. “But that’s exactly what a partisan power grab would guarantee. And that’s what (this bill) is all about.”

States including Georgia, Florida, Arizona and Texas are pushing new voting rules, spurred by former President Donald Trump’s false claims about election fraud after his 2020 loss.

Democrats are on defense, having been unable to halt the onslaught of new state rules that will take months or years to litigate in court. That leaves passage of legislation through Congress as one of the few remaining options to counteract the GOP efforts.

“These bills moving in state capitals across America are not empty threats, they are real efforts to stop people from voting,” said Sen. Amy Klobuchar, a Minnesota Democrat and chairwoman of the Senate Rules Committee.

But Sen. Roy Blunt, R-Mo., the top Republican on the panel, predicted the bill, if passed, would yield an “unmitigated disaster” in future elections where “chaos will reign.”

Republicans argue the new state rules are needed to clamp down on mail ballots and other methods that became popular during the pandemic, but critics warn the states are seeking to reduce voter access, particularly for Black voters, ushering in a new Jim Crow era for the 21st century.

There was no widespread fraud in the 2020 election. Trump’s claims were rejected by Republican and Democratic election officials in state after state, by U.S. cybersecurity officials and by courts up to the U.S. Supreme Court. And his attorney general at the time said there was no evidence of fraud that could change the election outcome.

McConnell wasn’t the only high-profile figure at Tuesday’s hearing. Senate Majority Leader Chuck Schumer, D-N.Y., also spoke during the Rules panel meeting to add his weight to the debate.

“Instead of doing what you should be doing when you lose an election in a democracy, attempting to win over those voters in the next election, Republicans instead are trying to disenfranchise those voters,” Schumer said, his voice rising. “Shame on them!”

President Joe Biden has said the federal legislation would “restore the soul of America” by giving everyone equal access to the vote.

The legislation, known as the For the People Act, was given top billing on the Democratic agenda, but the path ahead is unclear. Moderate members of the Democratic caucus also pose a sizable obstacle to the bill becoming law.

Sens. Joe Manchin of West Virginia and Kyrsten Sinema of Arizona have both said they oppose making changes to the Senate’s filibuster rules, which would be needed to maneuver the bill past Republican opposition and pass it with a simple majority in a 50-50 Senate, with Vice President Kamala Harris delivering the tiebreaking 51st vote.

Manchin has called for any elections overhaul to be done on a bipartisan basis. Other Democrats want to pare back the bill to core voting protections to try to put Republicans on the spot.

Both Manchin and Sinema were getting face time with President Joe Biden this week, as their votes are also vital to passing the president infrastructure plan. Manchin came to the White House on Monday, while Sinema was slated to do so on Tuesday, according to the White House.

House resolution H.R. 1, and its companion, S. 1, in the Senate have been in the works for several years. As passed by the House in March, the legislation would create automatic voter registration nationwide, require states to offer 15 days of early voting, require more disclosure from political donors and restrict partisan gerrymandering of congressional districts, among other changes. It would also compel states to offer no-excuse absentee voting.

It would force the disclosure of donors to “dark money” political groups, which are a magnet for wealthy interests looking to influence the political process while remaining anonymous.

Democrats have been making their own changes to the bill to draw support.

In the latest version of the legislation, states would have more time and flexibility to put new federal rules in place. Some election officials had complained of unrealistic timelines, increased costs and onerous requirements.

States would have more time to launch same-day voter registration at polling places and to comply with new voting system requirements. They would also be able to apply for an extension if they were unable to meet the deadline for automatic voter registration. Officials have said these are complex processes that require equipment changes or upgrades that will take time.

Democrats are also dropping a requirement that local election offices provide self-sealing envelopes with mail ballots and cover the costs of return postage. They plan to require the U.S. Postal Service to carry mail ballots and ballot request forms free of charge, with the federal government picking up the tab.

—Cassidy reported from Atlanta. Associated Press reporter Jonathan Lemire contributed reporting.