The Missouri referendum on the 2025 Republican-drawn congressional map (Proposition A, or HB 1) appears on the November 3, 2026 ballot after the state Supreme Court unanimously ruled on September 3 that the measure qualifies and suspended the new lines pending voter approval, reverting to 2022 boundaries for the general election. The secretary of state certified the referendum on September 8 following the decision, though further appeals remain possible. Traders assign a 55% probability to rejection in part because opponents gathered over 300,000 signatures to qualify the measure, Missouri voters have historically blocked legislative redistricting changes via referendum, and the map originated as a mid-decade partisan adjustment aimed at altering the state's congressional delegation. The outcome hinges on turnout and messaging around direct democracy and district boundaries.