Voters walk to a polling station in Tempe, Ariz., in November 2020.

Matt York/AP

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Matt York/AP

The U.S. Supreme Court is allowing Arizona to enforce for now part of a new state law that requires election officials to reject any state voter registration forms that are submitted without the applicants’ proof of U.S. citizenship.

The high court, however, has rejected the Republican National Committee’s request to block what could have been tens of thousands of registered voters in Arizona from voting in this fall’s presidential election.

The high court’s order, released Thursday, is part of a legal fight over voter registration requirements in the key swing state, where in 2020, President Biden defeated former President Donald Trump with just over 10,000 votes.

The ruling comes before what is expected to be a close presidential election — and amid a growing GOP push for voters to show proof of their U.S. citizenship when signing up to cast a ballot in federal elections, which many election experts warn could make voting more difficult for many eligible voters.

Arizona has a complicated, two-track system for registering voters, which stems from a decades-long dispute over the need for proof of citizenship.

State law requires showing documentary proof when registering to vote in state and local elections. But for federal elections, the Supreme Court ruled in 2013 that the state had to accept and use a standard federal form required by the National Voter Registration Act. That form does not require proof but calls for applicants to swear under penalty of perjury that they are U.S. citizens.

In 2022, however, Arizona’s GOP-controlled legislature passed a new law that bans registered voters who have not provided proof of their citizenship from voting in presidential elections or by mail for any federal office.

The U.S. Justice Department and civil rights organizations led by Mi Familia Vota sued, and following a 10-day trial, U.S. District Judge Susan Bolton struck down that restriction after finding that it is preempted by the National Voter Registration Act, which Congress passed in 1993 to make the registration process easier for eligible voters. Bolton’s decision cited a 1976 Supreme Court decision that said the high court has recognized “broad congressional power to legislate in connection with the elections of the President and Vice President.”

The Republican National Committee, along with Arizona’s top GOP state lawmakers, appealed Bolton’s ruling to the 9th U.S. Circuit Court of Appeals. The Republicans argue that the U.S. Constitution’s Electors Clause limits Congress’ role in regulating presidential elections and that Arizona’s state legislature has, as attorneys for the RNC and the GOP lawmakers wrote in a Supreme Court filing, “sovereign authority to determine the qualifications of voters and structure participation in its elections.” Still, this month, a panel of 9th Circuit judges declined to put a pause on the lower court’s ruling.

According to the Arizona secretary of state’s office, 42,301 voters in the state were registered for only federal elections, as of July 1.

Whether those registered voters are allowed to vote in future presidential elections after this fall’s race without showing proof of citizenship remains an open legal question. Oral arguments before the 9th Circuit are scheduled for Sept. 10 in San Francisco, and attorneys for the RNC have signaled in court filings they’re preparing to eventually ask the Supreme Court to take up this case.

Edited by Benjamin Swasey