Missouri voters will decide Proposition A on November 3, 2026, a veto referendum on House Bill 1, the 2025 congressional map drawn by Republican lawmakers during a special session at the urging of President Trump. The measure, certified for the ballot after a unanimous Missouri Supreme Court ruling in early September, would uphold new district lines that split Kansas City across three Republican-leaning seats and aim to deliver seven of eight congressional districts to the GOP. The 2022 map remains in effect for the current election following U.S. Supreme Court action. Traders assign a 74% probability to rejection, reflecting the mid-decade partisan redraw, successful collection of more than 300,000 opposing signatures by groups like People Not Politicians, and Missouri’s precedent of voters blocking legislative redistricting plans through referendum. Late Republican campaign efforts face a compressed timeline before early voting begins.