The Missouri congressional redistricting referendum, known as Proposition A, appears on the November 3, 2026 ballot as a veto referendum on House Bill 1, the 2025 Republican-drawn map that splits the Kansas City area across multiple districts in a shift from the 2022 lines. Following the Missouri Supreme Court’s unanimous September ruling that the measure qualifies for the ballot and that the new map cannot take effect without voter approval, traders assign the “no” outcome a 64.5% implied probability. This positioning reflects the plan’s origin in a mid-decade partisan effort, the collection of more than 300,000 signatures by opponents, and Missouri voters’ prior record of using referendums to reject legislative redistricting changes. Ongoing federal appeals and the use of 2022 maps for the current election cycle add further uncertainty ahead of the vote.