Democrats Now 60% Senate, 90% House Favourites on Prediction Markets — Biggest Shift Since 2024
Kalshi and Polymarket have moved sharply toward Democratic control of both US congressional chambers ahead of the 3 November midterms. Democrats are priced at ~60% to win the Senate and ~90% to win the House. Republicans held 80%+ Senate control odds when markets opened in November 2024. The shift started in February 2026 with the Iran war and has accelerated with rising gas prices and declining Trump approval ratings.
Prediction markets on Kalshi and Polymarket have repriced the 2026 US midterm elections substantially toward Democratic control over the past six months. As of September 21, Democrats are at approximately 60% to win Senate control and roughly 90% to win House control ahead of the 3 November elections. Republicans entered 2026 with Senate control odds above 80%, reflecting structural Senate map advantages — Democrats are defending 23 seats to Republicans' 12. The reversal represents one of the largest sustained prediction market price movements in a contested US election since the platforms began offering electoral contracts at scale.
For UK readers, the US midterm structure is analogous to a UK general election where one party must win a disproportionate number of marginal seats against a headwind. Democrats need a net gain of one seat to reach 50-50 (plus the Vice President's tie-breaking vote), or two seats for an outright majority. The Texas Senate race — a deep-red state where the incumbent Republican is now contested — is the highest-volume individual Senate race on Kalshi, suggesting the market is pricing genuine competitive uncertainty in seats that were not on the board 12 months ago. The Iran war in February 2026 was the proximate cause of the reversal: higher energy prices degraded consumer sentiment, and Trump's approval ratings fell below 45% for the first time. The historical pattern of midterm elections punishing the president's party in a deteriorating economic environment now favours Democrats in most probability models.
House control pricing is more decisive at ~90% Democratic. The historical pattern for House midterms when presidential approval is below 45% is strongly in the opposition party's favour; the House market is essentially pricing this as a near-certain Democratic gain. The Senate remains competitive despite the aggregate Democratic lead because the individual seat map still forces Democrats to win in multiple states where the Republican structural base is strong. More than 500 active midterm markets across Kalshi and Polymarket combined track individual races, balance of power scenarios, and vote-share outcomes — Polymarket's 'Balance of Power' event market gives Democrats Sweep at 61%, Republican Senate with Democratic House at 31%, and Republicans Sweep at just 8%.
The regulatory implications for prediction markets are acute if the markets are correct. A Democratic Congress taking office in January 2027 would face a SCOTUS ruling on the CFTC preemption question sometime in the June 2027 term — and if the Court rules against Kalshi, a Democratic Congress would be more likely to codify that outcome than to pass legislation reversing it. The sector's legal fate in 2027-2028 therefore depends on a simultaneous triple scenario: SCOTUS grants cert, rules in Kalshi's favour on the preemption question, and the result holds against a Democratic Congress that might otherwise legislate restrictions. Prediction markets currently price the combination of those outcomes at well below 50%. The prediction market sector's platforms are, in this specific case, accurately pricing the possibility that their own regulatory environment deteriorates significantly over the next 18 months — a demonstration of the information aggregation function the platforms claim to provide.
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Recent updates
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SCOTUS September 28 Long Conference: First Opportunity to Take the Prediction Market Case
The Supreme Court's September 28 'long conference' — its first sitting of the new term — is the first formal opportunity for justices to consider cert petitions from New Jersey (filed 2 Sep, Third Circuit) and Robinhood (filed 9 Sep, Ninth Circuit). Kalshi has 30 days to respond to NJ's petition. Polymarket prices a 46% chance SCOTUS accepts by year end. Most analyst projections place a cert decision between November and December 2026.