2026 Maine Senate Race

Maine is the Republicans' hardest Senate hold and the Democrats' clearest pickup: Susan Collins, seeking a sixth term in a state Democrats carried in every presidential election since 1992, against Troy Jackson, the former state Senate president who cleared the Democratic field in June.

The party book prices Jackson at 66% and Collins at 36%. That is not a typo and it does not sum to one—the two legs of a two-candidate book add to 102%, an arbitrage-free violation that survives because almost nothing trades on the Democratic side.

Almost all the flow is Collins. Of the $51,362 that changed hands in a day, $46,810 sits on the Collins leg—ninety-one percent of the book on the side the market gives one chance in three. Jackson's leg took $4,552.

And a third Kalshi book contradicts both. The margin Cumulative prices Democrats by 1 or more points—effectively "Jackson wins"—at 54%, a full twelve points below the 66% the party book gives him. Three books, one question, three answers. This is what a thin market on a well-known race looks like.

Kalshi runs the race twice: once by party and once by named candidate. The person book is the internally consistent one—Jackson 64%, Collins 36%, summing to 100—which makes the party book's 102% the outlier rather than a pricing view.

Collins and Jackson priced directly. Collins at 36% carries $46,810 of the day's $51,362; her leg also holds $1.30 million in open interest against Jackson's $820,912. On the person book the split is starker still—$5,309 on Collins against $85 on Jackson.

A book where the favorite's leg trades almost nothing is not a market that is confident. It is a market where one side has nobody to sell to.

The Cumulative on how large a Democratic win would be: 1+ points at 54%, 3+ at 45%, 5+ at 32%, 7+ at 26%, 9+ at 10%, 11+ at 12%. Note the 9+ and 11+ legs are inverted—11 points prices above 9 points, which is impossible in a properly-ordered cumulative chain.

Take the 54% at face value and the market's real estimate of a Jackson win is closer to a coin flip than the 64–66% the outright books show.

Adjacent books that price Maine as part of something larger. The Maine–Texas Senate combo pays on both races jointly, which is the cleanest read on whether the market thinks the two flip together. Manifold's multi-race book is the only non-Kalshi coverage of this seat anywhere.

• Three books, twelve points apart. Party book 66% Jackson, person book 64%, margin ladder 54%. Any of the three could be the mispriced one; the margin ladder is the thinnest, but it is also the only one that forces a distributional answer.
• The 102% party book is free money on paper. Buying No on both legs of a two-outcome Categorical at these prices locks a return. That it persists is the clearest possible evidence of how little size this market will absorb.
• Collins carries the flow and the open interest. $46,810 of $51,362 in a day and $1.30M of standing position. The trade being expressed here is that a six-term incumbent with a personal brand survives a bad national environment—again.
• Maine is the tiebreaker seat. It appears in the closest-race book and in the Maine–Texas combo precisely because the Senate majority runs through it. Watch those two reprice before the outright does.
• Nobody else lists it. Polymarket and PredictIt have no Maine Senate book. Manifold's multi-race Multiple is the entire cross-exchange picture, at $248 a day.