The GOP continues a legal fight against mail ballots that arrive after Election Day

Ahead of this year's election, Republicans have been trying to stop some states — including swing state Nevada — from counting postmarked mail ballots that don't make it to election officials until after Election Day.

That legal effort hasn't been going well. But Republican Party officials say they are committed to these challenges and in recent days they appealed their case in Mississippi to a conservative circuit court in the hopes of getting a favorable ruling there.

Roughly 20 states plus Washington, D.C., accept and count mail-in ballots that are received after Election Day if they are postmarked on or before Election Day. These rules are meant to accommodate voters who don't remember to turn in their ballot until Election Day and to create wiggle room in case there are issues with the Postal Service.

So far the Republican National Committee and others have filed ballot return challenges in Nevada, Illinois, Mississippi and North Dakota.

Early this year, the North Dakota case was thrown out of court. And last month, judges in Mississippi and Nevada also threw out the lawsuits filed by the RNC aiming to disqualify ballots that arrive after Election Day.

The RNC has argued that rules allowing ballots to be counted after Election Day violate federal law. The party argues that Congress — not states — decides when a federal election ends.

Claire Zunk, communications director for the RNC's election integrity unit, told NPR in a statement that "the election should end on Election Day - that's the law, and voters deserve fair and accurate results on November 5th."

She added: "Counting ballots that come in after Election Day in Mississippi and other states threatens election security and undermines transparency for voters."

In the Mississippi case, GOP-appointed federal Judge Louis Guirola ruled that Congress made allowances in some cases for ballots that arrive after Election Day, so the state's laws are not in violation.

"If one federal statute implicitly allows post-election receipt of overseas ballots mailed by election day, that statute is presumed not to offend against the election-day statutes," the judge wrote, "from which one may infer that the similar Mississippi statute on postelection receipt is likewise inoffensive."

And now the RNC has appealed the Mississippi case to the 5th U.S. Circuit Court of Appeals, which is known as perhaps the most conservative appeals court in the United States.

Zunk told NPR that the RNC also plans to appeal the Nevada case.

"Rather than letting us fight this in court, a liberal judge unjustifiably dismissed our case," Zunk said. "Political parties must be allowed to fight invalid election laws that threaten the integrity of our elections."

The stakes for Nevada's case are particularly high because elections are so close in the state. Furthermore, large numbers of voters now cast ballots by mail thanks to Nevada's universal mail ballot program.

Joe Biden beat then-President Donald Trump in Nevada in 2020 by about 33,500 votes. During the 2022 midterm elections, in Clark County alone — the county where Las Vegas is — state officials say about 40,000 valid ballots came in after Election Day.

Democrats and voting rights advocates have called these kinds of lawsuits "fringe" and an effort to undermine U.S. elections. They also say it's part of a larger effort to shorten the windows during which voters can return their mail ballots.

The Democratic Legislative Campaign Committee said this summer that it has tracked at least 47 bills across 18 states in the 2023 and 2024 legislative sessions that would shorten ballot return windows.