In Nevada, the Trump campaign filed a lawsuit this week seeking images of the signature of every registered voter in Democratic-leaning Clark County — a potential first step toward challenging individual votes on grounds that the signed ballots don't match the signatures on file.

In Texas, Republican officeholders and candidates sued this week to have more than 100,000 votes invalidated in the Houston area because they were cast at drive-through voting centers the GOP has asked a judge to declare illegal.

And in Minnesota and Pennsylvania, election officials will set aside any mail-in ballots that arrive after Election Day — even if they were mailed before the polls closed — to facilitate potential court challenges.

For months, Republicans have pushed largely unsuccessfully to limit new avenues for voting in the midst of the pandemic. But with the election rapidly approaching, they have shifted their legal strategy in recent days to focus on tactics aimed at challenging ballots one by one, in some cases seeking to discard votes already cast during a swell of early voting.

"It's not just the rules anymore," said Myrna Pérez, director of the Voting Rights and Elections Program at the nonpartisan Brennan Center for Justice. "It's individual voters."

Republicans said they are just trying to make sure the process runs smoothly and the rules are applied fairly, arguing that Democrats have loosened election rules in ways that could confuse voters and invite fraud.

"We have volunteers, attorneys and staff in place to ensure that election officials are following the law and counting every lawful ballot," Justin Riemer, chief counsel for the Republican National Committee, said Friday. "If election officials aren't providing transparency that the law demands or we are unable to resolve disputes over certain ballots or procedures, then we will litigate as necessary."

But Democrats said there is no evidence that expanded mail balloting and other pandemic-related changes lead to fraud. They accused Republicans of targeting valid votes in Democratic strongholds in a blatant bid to gain an electoral advantage.

"The other side has given every indication that they will challenge every ballot they can, at every step of the process," said Chad Dunn, general counsel for the Texas Democratic Party and co-founder of the UCLA Voting Rights Project.

"The mask is off. This isn't about rooting out any mythical voter fraud. It never was," Dunn said. "This is about raw power and obtaining power by any means necessary."

The shift in strategy comes after Republicans largely failed to limit expanded access to absentee balloting aimed at ensuring people could vote safely during the pandemic. In late September, a Washington Post review of 90 state and federal voting lawsuits found that judges had been broadly skeptical of GOP claims that the possibility of voter fraud required limits on mail balloting.

More than 90 million people have already voted, many using mail-in ballots. But President Donald Trump has spent months trying to undermine confidence in mail ballots, and polls have consistently shown that more Republicans plan to vote in person on Election Day while many Democrats have chosen to vote absentee.

That means Republicans stand to gain a significant advantage if they can successfully challenge absentee votes already cast. Trump has telegraphed for months that if the election is close and he is running ahead of former Vice President Joe Biden on election night, he will urge states to stop counting absentee ballots, even if they have been correctly cast.

"It would be very, very proper and very nice if a winner were declared on Nov. 3, instead of counting ballots for two weeks, which is totally inappropriate and I don't believe that that's by our laws," Trump told reporters at the White House last week.

Speaking to donors at a closed-door fundraiser in Nashville last week, Trump said his campaign would have his own "team" and law enforcement watching polling places, and that the campaign would probably have to challenge individual ballots. "My biggest risk of losing is probably fraud," he said, according to one person in the room, who spoke on the condition of anonymity to describe the private event.

A senior Trump campaign official said they are most closely watching Nevada's Clark County, Philadelphia and Milwaukee — all Democratic strongholds in swing states — as well as the entire state of North Carolina.

RNC spokesman Mike Reed denied Democratic claims that the party is trying to discourage voters, noting that the GOP has run an expansive get-out-the-vote program. Though last-minute rules changes championed by Democrats invite "fraud and postelection confusion," he said, "we want every vote that is legally eligible to be cast and counted safely and securely."