**Missouri voters will decide Proposition A, a veto referendum on the 2025 Republican-drawn congressional map (HB 1), on November 3, 2026.** The measure, certified for the ballot after the state Supreme Court’s unanimous September 3 ruling and the secretary of state’s September 8 certification, asks whether to uphold new district lines that adjust boundaries in the Kansas City area. A “yes” vote would enact the map for future elections; a “no” vote would retain the 2022 lines. Traders assign “no” a 57.5% implied probability, reflecting Missouri’s precedent of rejecting legislative redistricting changes via referendum in most prior cases, the collection of over 300,000 signatures by opponents, and the map’s origin as a mid-decade partisan redraw. Ongoing appeals to federal courts introduce some uncertainty but have not altered the ballot placement.