The Missouri Supreme Court unanimously blocked a congressional map backed by President Donald Trump from being used in November's midterm elections, restoring the state's previous districts unless voters approve the new boundaries.
The ruling handed Republicans a setback in the nationwide redistricting battle and came just two months before the general election, after the disputed districts had already been used for Missouri's August primaries.
Republican officials pledged to appeal the decision to the US Supreme Court.
The dispute centers on congressional districts signed into law in September 2025 after Missouri's Republican-led legislature moved to redraw the map.
The boundaries were designed to improve Republican prospects of gaining another US House seat, particularly by reshaping the Kansas City-based 5th Congressional District held by Democrat Emanuel Cleaver.
Opponents responded by gathering nearly 300,000 signatures seeking a statewide referendum on the map.
Secretary of State Denny Hoskins rejected the petition on August 4, the day of the party primaries, arguing that the referendum process could not be used for congressional redistricting.
A lower court agreed, but the state Supreme Court overturned that decision.
"The referendum petition was legal, sufficient, and timely, and the secretary incorrectly concluded otherwise," the court ruled.
The judges found that Missouri's constitutional referendum provision covering legislative acts also applied to congressional redistricting.
The court determined that the 2025 legislation did not take effect because of the valid referendum petition and cannot be used unless voters approve it.
Consequently, the congressional map adopted after the 2020 census remains in effect for November's election.
The decision creates an unusual situation because Missouri conducted its primaries under districts that cannot currently be used in the general election.
Missouri Attorney General Catherine Hanaway said the state would immediately appeal to the US Supreme Court, while Trump denounced the ruling.
Republicans had argued that reverting to the previous districts so close to the election could cause confusion.
The decision follows a broader mid-decade redistricting push encouraged by Trump, with Republican-led states seeking electoral advantages and California adopting boundaries favoring Democrats.
Missouri's legal fight now moves toward a possible federal appeal as election officials prepare for November.