WASHINGTON — Senate Republican leader Mitch McConnell is so determined to stop a sweeping elections overhaul pushed by congressional Democrats that he will personally argue against it, armed with a stack of amendments at a Senate hearing this week as Democrats advance the bill toward a vote.

It’s a rare role for a party leader but shows the extent to which Republicans are prepared to fight the Democratic priority. The legislation would be the largest overhaul of U.S. elections in a generation and touches on almost every aspect of the electoral process, changes that Democrats argue are even more important now as states impose new voting restrictions after the divisive 2020 election.

What’s typically an hourslong legislative slog could drag into a dayslong showdown starting Tuesday at the Senate Rules Committee, a surprising new venue in the nation’s broader debate over voting rules.

The action in Congress comes as states including Arizona, Florida, Georgia 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.

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 is expected to be an “active” participant in Tuesday’s session to debate and amend the voting bill, his office said. Stopping the bill is his “priority,” as Republicans argue the legislation represents a Democratic power grab and federal overreach into state administration of elections.

Senate Majority Leader Chuck Schumer, D-N.Y., is also expected to stop in at the rules panel meeting to add his weight to the debate. 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. Despite the showing from McConnell, who has cultivated a reputation for turning the Senate into a legislative graveyard, 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 in order 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.

The House resolution and its companion 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.

It would also compel states to offer no-excuse absentee voting.

In particular, 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.

McConnell has spent a career fighting for the free flow of campaign cash as a constitutionally protected right to free speech.

One GOP aide who spoke on condition of anonymity to discuss the situation candidly said they are planning to try to strike out full sections of the bill and introduce other changes.

Democrats have been making their own changes to the bill to draw support. Manchin has not yet signed on, and his backing will be crucial.

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 to get in place.