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.

Kalshi's party book prices Jackson at 59.5% and Collins at 40.5%. Three weeks ago it was 66 / 36, a book that summed to 102%; it now sums to 100, and Jackson has given back six and a half points.

The flow is no longer one-sided. Of the $202,973 that changed hands in a day, four times the volume of three weeks ago, $122,145 traded on Jackson and $80,828 on Collins. In mid-September 91% of the book was on Collins.

The books have converged, and a second exchange has arrived. Kalshi's person book prices Jackson at 55.5% and its margin Cumulative prices Jackson by 1 or more points at 53%; three weeks ago the spread between Kalshi's highest and lowest read was twelve points, and it is now six and a half. Polymarket lists the race at 58.5% for Jackson, a point under Kalshi's party book.

Kalshi runs the race twice: once by party and once by named candidate. The party book has Jackson 59.5%, Collins 40.5%; the person book has Jackson 55.5%, Collins 43.5%, with Graham Platner, Janet Mills and Nirav Shah at 0.1% each. The party book is the deeper one: $202,973 today against $16,625.

Below them, Polymarket's book on the same race: Jackson 58.5%, Collins 40.5%, on $19,710, with $12,733 of it on Collins. The two exchanges are a point apart on Jackson and agree on Collins.

Collins and Jackson priced directly. Jackson at 59.5% took $122,145 of the day's $202,973; Collins at 40.5% took $80,828. The standing positions still lean the other way: Collins's leg holds 2.0 million contracts of open interest against Jackson's 1.13 million. On the person book the day split $9,758 on Jackson against $6,842 on Collins.

Three weeks ago the favorite's leg barely traded. It is now the busier of the two, at a lower price.

The Cumulative on how large a Jackson win would be: 1+ points at 53%, 3+ at 40%, 5+ at 24.5%, 7+ at 18.5%, 9+ at 9.65%. The ladder is in order now; three weeks ago its top rungs were inverted. It turned $1,255, $953 of it on the 3+ rung.

Take the 53% at face value and the market's estimate of a Jackson win is close to a coin flip, six and a half points under the party book. Beside it, the closest-race board: Texas 16.5%, Iowa 16%, Kansas 9.5%, Maine 9.15%.

Adjacent books that price Maine as part of something larger. The Maine–Texas Senate combo pays on both races jointly: Talarico and Jackson is 45%, Paxton and Collins 28.5%, Talarico and Collins 16.5% and Paxton and Jackson 11.5%, on $52,113, more than half of it on the double Republican hold. Its Jackson legs add to 56.5%, between the person book and the party book. Beside it, Manifold's multi-race book, which turned $61.

• Three Kalshi books, six and a half points apart. Party book 59.5% Jackson, person book 55.5%, margin ladder 53%. Three weeks ago the spread was twelve points; the books have converged on a closer race.
• Jackson has given back ground. 66% to 59.5% on the party book and 64% to 55.5% on the person book since mid-September.
• Collins holds the open interest. 2.0 million contracts against 1.13 million on the party book. The trade being expressed is that an incumbent with a personal brand survives a bad national environment again.
• Maine is a tiebreaker seat. It appears in the closest-race book at 9.15% and in the Maine–Texas combo because the Senate majority runs through it. Watch those two reprice before the outright does.
• A second exchange now lists it. Polymarket prices Jackson at 58.5% on $19,710 a day, a tenth of Kalshi's party book. Manifold covers the seat only inside its multi-race Multiple.