2028 Democratic Nomination — Cross-Exchange

The 2028 Democratic nomination is the deepest durable book in prediction markets: $1,370,681 a day on Kalshi against $447,504 on Polymarket, with more than $4 million of open interest sitting on individual legs. Nobody votes for two and a half years. The book trades anyway.

Three names now lead, and the third one is new. Alexandria Ocasio-Cortez holds the top slot at 17% on Kalshi and 20.1% on Polymarket, having taken it from Gavin Newsom earlier this summer. Newsom is second at 16.1% on both. The change since this workspace was last rebuilt is Jon Ossoff at 14–15%, up into a near-tie for second on both exchanges from outside the top five.

And the volume is somewhere else entirely. Andy Beshear trades at 3.8% on Kalshi and carries $138,380 in a day—twice AOC's $68,888 and more than the top three legs combined. Ninth in price, first in flow, on both books. The Kentucky governor is the position this market is quietly accumulating.

The two exchanges agree on the ordering and disagree on the level: Polymarket prices AOC three points richer and Kamala Harris nearly two points cheaper. On a book this deep those gaps persist rather than close.

Kalshi and Polymarket run the same question at three times the size on Kalshi. Read them side by side for the level disagreements—the ordering is identical through the top four.

The front of the book priced directly on each side. AOC at 17% on Kalshi against 20.1% on Polymarket—a three-point spread on the single most-weighted outcome, and it has been stable rather than converging. Kalshi's leg carries $4.31M of open interest, the largest single position anywhere in this market.

Newsom at 16.1% and Ossoff at 14% on Kalshi—inside the bid-ask on most sessions. Ossoff's climb is the structural change in this book since spring: a first-term senator from a state that has flipped twice, priced ahead of Harris, Buttigieg, Shapiro and Pritzker.

Andy Beshear at 3.8% took $138,380 in twenty-four hours. For scale: AOC's leg took $68,888, Newsom's $41,038, Ossoff's $26,161. One leg priced under four cents carried more flow than the entire top three.

Polymarket shows the same asymmetry in miniature—Beshear at 2.2% with $10,045 against Ossoff's 15% and $8,763. When two independent books put outsized flow on the same longshot, that is usually accumulation rather than noise.

Adjacent books that extend the story. The Democratic VP nomination trades at $9,581 a day, and Manifold runs an independent nominee book that is worth reading as a crowd check against the two big exchanges—it has repeatedly led Kalshi on repricings by a few days.

• Ossoff into the top three is the real move. He is priced ahead of Harris, Buttigieg, Shapiro and Pritzker on both exchanges. His 2026 Senate re-election in Georgia is the event most likely to reprice this leg in either direction.
• Beshear's flow is not matched by his price. $138k a day at 3.8% on Kalshi, plus the deepest longshot flow on Polymarket. Either the accumulation is right and the price follows, or it is a large hedge against the progressive legs—there is no third reading.
• AOC's three-point cross-exchange spread is durable. 17% Kalshi against 20.1% Polymarket. On a book turning over $1.8M a day across both venues, a persistent gap of that size on the leading outcome says the two user bases genuinely disagree.
• Nothing here settles for two and a half years. Every position carries multi-year carry cost. The open interest—over $4M on several individual legs—means holders are financing that, which is itself a signal about conviction.
• Watch the 2026 midterms as the first real information event. Senate outcomes in Georgia, Michigan and North Carolina reprice several of these names directly; a bad night for the party repices all of them.