Missouri voters will decide Proposition A, a veto referendum on the Republican-led HB 1 congressional map, on November 3, 2026. The measure qualified after the state Supreme Court unanimously ruled in early September that the constitution permits referendums on such acts, overriding the secretary of state's prior rejection and blocking the new lines for the 2026 elections. Traders assign "No" a 56.5% implied probability, reflecting the map's mid-decade partisan origins aimed at shifting Kansas City districts, the collection of over 300,000 signatures by opponents, substantial campaign funding on both sides, and Missouri voters' history of rejecting legislative redistricting plans at the ballot. An appeal to the U.S. Supreme Court remains possible but has not altered the current November timeline.