After a record number of Americans chose to cast their ballot by mail in 2020, Republican-led states and Democrat federal lawmakers are fighting a pitched battle over the rules governing the future of voting in the United States -- with special attention on whether voters will still be permitted to send their ballots through the mail.
This "great clash," as it is framed by Michael Waldman, president of the bipartisan Brennan Center for Justice public policy institute, pits multiple Republican-controlled state legislatures pushing bills for tighter restrictions against a Democrat-dominated federal government that has pressed ahead with a nationwide voting rights package.
"In states across the country, Republican legislatures are racing to enact restrictions on voting rights -- the most significant wave of such restrictions since the Jim Crow era," Waldman said. Conversely, said Waldman, Congress "can supersede that voter suppression wave, can override those laws."
At the heart of the fight is the widespread use of mail-in ballots. Voting by mail has been pushed by advocates for years, but the practice exploded in 2020 as a way to address the challenges of holding elections during the global coronavirus pandemic. Then-President Donald Trump seized on the practice -- both before and after his defeat -- to push unsupported claims that mail-in ballots are subject to greater risk of fraud, something experts have refuted.
Since January, more than 250 bills that would restrict access to voting have been introduced in 43 statehouses, according to Brennan Center for Justice officials. The "biggest chunk" of these proposals would "limit who can vote by mail and how easy it is to vote by mail," said Eliza Sweren-Becker, counsel in the Brennan Center's Democracy Program.
"Policymakers are essentially trying to put stumbling blocks in the way of voters in every step of the way in the mail voting process," Sweren-Becker said.
Much of the legislation being considered aims to slash recent rules that broadened access to voting by mail during the pandemic, such as no-excuse absentee voting and extended deadlines for ballots sent through the U.S. Postal Service.
Opponents of these recent rules say that changes made during the pandemic were not intended to be permanent. And they want to ensure that the act of in-person voting at polling precincts is not supplanted by more remote methods.
"Certainly some states want to reign in the practice pretty dramatically," said Jason Snead, the executive director of the Honest Elections Project, which is advocating for tighter election laws, "but most of the conversion is how we make this process work well and how to we secure this process."
"What we're talking about is the basic need to safeguard the process, and to show voters that the process has integrity can be trusted," Snead said.
The battle is particularly fierce in places like Arizona and Georgia, key battlegrounds where Democrat Joe Biden carried the vote, but Republicans maintain control of state government.
In Arizona, for example, one bill introduced by Republican legislators would require absentee ballots to be returned in person, not by mail. Conversely, another bill seeks to effectively ban the use of drop boxes and drive-through ballot drop-offs by mandating that absentee ballots can only be returned through the mail.
"So even within a single state sometimes there's a real conflict in the type of legislation being introduced," said Tammy Patrick, a senior adviser at the Democracy Fund, a nonpartisan election advocacy group.
Following the election, Arizona Gov. Doug Ducey defended the state's election integrity in the face of criticism from Trump and others. "I trust our election system. There's integrity in our election system," Ducey said in an interview in December.
On Monday in Georgia -- where increased turnout helped Biden win the presidency in November and two Democrats win the state's Senate seats in January -- the Republican-controlled state legislature approved a new measure to change the state's absentee voting laws over the objections of Democrats and voting rights advocates.
"I felt like there were not any unreasonable changes that were made," Republican state representative Dale Washburn said of the bill. "[It] should provide more security and more confidence in the system."
Georgia Secretary of State Brad Raffensperger, a Republican, has repeatedly said there was no evidence of fraud in the state's election. "We've never found systemic fraud, not enough to overturn the election," Raffenseperger told ABC's George Stephanopoulos in December.
Because Republicans control the levers of powers in both Arizona and Georgia, Sweren-Becker said, legislation aimed at curbing mail-in voting is expected to pass in some form.
Yet in Washington, where Biden is in the White House and Democrats now have majorities in both chambers of Congress, preserving access to absentee voting has emerged as a legislative priority.
On Thursday, the House of Representatives voted to pass H.R. 1, a sweeping voting rights bill that expands access to absentee voting with nationwide baselines. Democrats have cited Republican efforts to curb mail-in voting rules at the state level as the impetus for the legislation, which, if passed and enacted, would take precedence over statewide regulations during federal elections.
"We're not pursuing this reform against the backdrop of the status quo," the bill's lead sponsor, Rep. John Sarbanes, D-Md., told ABC News. "We're pursuing it against the prospect that the Republicans will take things in the wrong direction, and in a significant way."
Republican pushback to H.R. 1 has been swift and strong, with warnings that the bill's standards would usurp the states' constitutionally protected right to run their own elections.
On Thursday, 20 Republican state attorneys general warned that, if passed, the bill "would federalize state elections and impose burdensome costs and regulations on state and local officials."
Former Vice President Mike Pence, in an op-ed published this week in the Daily Signal, wrote that H.R. 1 would unfairly "force states to adopt universal mail-in ballots."
"Election reform is a national imperative, but under our constitution, election reform must be undertaken at the state level," Pence wrote.
Other experts fear that these statewide bills reflect partisan efforts to justify unsupported claims that the 2020 presidential election was undermined by widespread voter fraud.
"Lawmakers are using those lies to justify policies that limit voting access," Sweren-Becker said, calling it "disingenuous and misleading."
Sweren-Becker called efforts in GOP strongholds to change absentee voting rules a "backlash" to Trump's defeat.
Patrick, who said any so-called evidence of voter fraud underpinning these proposals is "not based on the facts," called 2020 "the most transparent election in our history."
"It was the most observed election; it was the most audited election," Patrick said. "There are definitely things that could and should be done to improve the process, but far too often the proposals being made are based on misinformation and lies."
In Georgia, where Black voters propelled Biden's victory due in no small part to expanded access to no-excuse mail-in voting, critics of the GOP's statewide voting proposals claim they will disenfranchise large swaths of Black voters, who overwhelmingly support Democrats.
"Democrats are more likely to be people of color," said Stacy Abrams, a Georgia-based voting rights advocate and former Democratic candidate for governor. "And so, whether [these bills] intend to target Democrats or not, they are absolutely targeting communities of color to silence their voices. But H.R. 1 would guarantee that, once again, we would have access to no-excuse absentee balloting."
ABC News' Benjamin Siegel contributed to this report.