Missouri must use its 2022 and 2024 congressional district boundaries in the November midterms after the U.S. Supreme Court on Sept. 25 blocked a Republican-backed map championed by President Donald Trump. The ruling is a setback for Republicans seeking to strengthen their narrow advantage in the U.S. House. The 2025 map would have shifted more Republican voters into the 5th Congressional District, potentially endangering Democratic Rep. Emanuel Cleaver. The justices warned that switching district lines during an election could cause “electoral chaos.” The decision means voters will cast ballots under boundaries different from those used in Missouri’s Aug. 4 primaries, when the Republican map was in effect. The dispute began after Missouri lawmakers approved the new map last year at Trump’s urging. Opponents gathered enough signatures to put a referendum on the November ballot. The Missouri Supreme Court ruled earlier this month that the referendum process meant the 2025 map had not become law, faulting Secretary of State Denny Hoskins for using it in the primaries before voters had approved it. Republicans then pursued the map in federal court, where a judge and an appeals court sided with them. The case returned to the U.S. Supreme Court, which rejected their position. Republicans argued that the map should remain in place because more than a million Missourians had voted in the primaries using those districts. Opponents countered that voters had not approved the map and said Republican officials had prolonged the process to force it through. The timing has left election administrators managing competing district lines as voting gets underway. Missouri officials began mailing some absentee ballots using the older boundaries the week before the ruling, while the primaries had used the newer map. The battle is part of a broader, Trump-backed effort to redraw congressional districts between the usual once-a-decade redistricting cycles. The effort shifted roughly nine or 10 districts nationally toward Republicans, as both parties maneuver for control of a closely divided House.