The U.S. Supreme Court is considering whether states can count mail-in ballots postmarked by Election Day but received afterward, focusing on Mississippi’s law allowing a five-day grace period. The Republican National Committee and others argue that federal law requires ballots to be received by Election Day, while Mississippi officials defend their law under the Constitution’s Elections Clause and warn that invalidating it could affect millions of voters, including military personnel. The ruling, expected before the November midterms, will address the tension between federal election uniformity and states’ authority over mail-in ballot deadlines.