MADISON, Wis. (AP) — Up to 2,000 voters in Wisconsin’s heavily Democratic capital of Madison were sent duplicate absentee ballots, but a city spokesperson said Tuesday that none had been returned, all affected voters were being contacted and there were multiple safeguards in place to ensure only one ballot is counted.

“This was a mistake,” city spokesperson Dylan Brogan said. “The clerk’s office moved to rectify it as quickly as possible.”

The error in a Democratic stronghold in the battleground state led to a demand for more information from U.S. Rep. Tom Tiffany, a Republican backer of former President Donald Trump whose northern Wisconsin district does not include Madison.

“Voters deserve clear answers regarding the full scope of this blunder, how the city plans to restore public confidence in its ability to accurately administer the election, and assurances that those responsible are held accountable,” Tiffany wrote.

The error in Madison and push for more information from a Trump backer comes as there is intense scrutiny over how elections are run, particularly in battleground states like Wisconsin. Trump lost Wisconsin in 2020. Nearly four years later, conspiracy theories surrounding the 2020 election and false claims of widespread fraud persist. Trump continues to insist, despite no evidence of widespread fraud, that he won that election as he seeks a return to the White House.

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President Joe Biden’s win over Trump in Wisconsin survived two recounts ordered by Trump, including one involving the city of Madison, an independent audit, a review by a Republican law firm and numerous lawsuits.

Brogan said election clerk Maribeth Witzel-Behl was in the process of responding to Tiffany’s letter and “thoroughly answering all of these questions.”

“It doesn’t matter if it’s Tom Tiffany, or who it is, we want everyone to know what happened,” Brogan said.

He said the mistake occurred when two identical files were merged, resulting in the creation of a list with double the names and double the addresses. Up to 2,000 duplicate ballots in one ward were mailed late last week before the mistake was caught and corrected, Brogan said.

The clerk’s office has been contacting voters individually to notify them of the error and cautioning them to submit only one ballot, Brogan said. However, because the ballots have identical barcodes, if two ballots are submitted, only the first one scanned will be counted, Brogan said.

Also, once the ballot is scanned, the voter is marked in the poll book as having submitted an absentee ballot. That is another safeguard against the voter submitting a second ballot, the clerk’s office said.

As of Monday, Madison had sent 27,421 absentee ballots and none had been returned, according to the state elections commission. Brogan said none of the duplicate ballots had been returned since then.