Arizona’s drawn-out Senate election has attracted a lawsuit from Republicans in the state, challenging the procedure for how mail-in ballots are counted.

Republican Martha McSally and Democrat Kyrsten Sinema, both U.S. representatives, are in a heated battle to become Arizona’s next senator. As of Thursday afternoon, McSally had 856,848 votes to Sinema’s 839,775, giving the Republican lawmaker a one-point edge with 99 percent of precincts reporting.

Despite the lead, election forecasters are not ready to declare McSally a winner because of the inordinate amount of mail-in ballots still not counted. About 75 percent of Arizona voters cast their ballots by mail, and county recorders are only beginning to wade through the 600,000-plus outstanding votes — a process that is expected to take days. (RELATED: It Could Be Days Until The Arizona Senate Election Is Decided)

While Arizona allows for an unusually high number of mail-in ballots, the confirmation for such votes is arduous. Votes by mail can be opened and counted only after a signature confirmation process is completed. A county is allowed to verify a voter’s identity if there is any issue with their mail-in ballot.

This confirmation process lies at the heart of the GOP lawsuit.

Four county GOP parties are claiming that county recorders are not following a uniform process in verifying mail-in ballots. They are also alleging two counties are improperly allowing these fixes after Election Day. The lawsuit seeks to stop the counting of ballots that were verified after the polls closed.

It’s unclear how many of these ballots are in play, but the lawsuit criticizes Arizona’s two most populous counties — where Sinema holds most of her support — for allowing voters to have as many as five days after the election to clear up any issues with their signatures.

McSally and Sinema are vying to replace outgoing Republican Sen. Jeff Flake, who announced in October 2017 that he would not seek re-election, acknowledging that he was too unpopular to win re-election. McSally, a former Air Force pilot, has campaigned on her military background closeness to President Donald Trump. Sinema, a former independent who aligned with the Green Party, has been forced to downplay her anti-war past as she’s campaigned in a red-leaning state.

The lawsuit is scheduled to be heard on Friday.

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