Will the Democrats win the Maine Senate race in 2026?

Crossbook compares what two exchanges, Polymarket and Kalshi, charge for the same event, and publishes a permanent scored record of its own forecasts under published rules.

Materially different settlement terms. No eligible price gap is available.

TradingContract settles 4 Nov 2026Last checked 29 Oct 2026, 18:30 UTC

Bid/ask midpoint · retrieved 2026-10-29T18:30:28.542Z. Venue quote-update time is unavailable. Readings can be asynchronous.

64.5%bid 63.0% / ask 66.0%24h volume $43K · liquidity $445Kas of 29 Oct, 18:30 UTCView on Polymarket

Bid/ask midpoint · retrieved 2026-10-29T18:30:29.218Z. Venue quote-update time is unavailable. Readings can be asynchronous.

62.5%bid 62.0% / ask 63.0%24h volume $60Kas of 29 Oct, 18:30 UTCView the event containing this market on Kalshi

How each venue defines this

Each exchange's own settlement text, quoted as written. Where they differ, the difference is usually why the prices do.

These two contracts name settlement dates about 2 months apart. Read both terms below for why: a later date can mean a different condition, a longer deadline or an administrative delay, and only the terms say which.

Settles Nov 4, 26

This market will resolve according to the winner of the 2026 midterm Maine U.S. Senate election, inclusive of any run-offs. A candidate shall be considered to represent a party in the event that he or she is the nominee of the party in question. Candidates other than the Democratic or Republican nominee (e.g., Greens, Libertarian, independent) may be added at a later date. Candidates who run as independents will not be encompassed by the “Democrat” or “Republican” options regardless of any affiliation they may have with the party. The candidates may be named in the contract for the convenie…

Settles Jan 4, 27

If a representative of the Democratic party is sworn in as a Senator of Maine for the term beginning in 2027, then the market resolves to Yes.

Settlement basis

Materially different settlement terms

Materially different: the two venues ask the same question in ordinary cases, but their contracts pay on different conditions. The deciding clauses and the difference are below. The price gap is not ranked.

“This market will resolve according to the winner of the 2026 midterm Maine U.S. Senate election, inclusive of any run-offs.”

“If a representative of the Democratic party is sworn in as a Senator of Maine for the term beginning in 2027, then the market resolves to Yes.”

Different conditions. Polymarket pays on who wins the election, as called by AP, Fox and NBC or by certification; Kalshi pays on who is sworn in for the 2027 term. They diverge if the winner is not seated — death, withdrawal, a contested certification — and Kalshi's contract runs two months longer, to the swearing-in in January. The gap between the two prices is not ranked as a like-for-like comparison.

Reviewed Oct 5, 26 under rules v1.3.

Confirmed as the same question: Will the Democrats win the Maine Senate race in 2026?

Crossbook forecast

55.0%against a market price of 67.5% at the timeOpen

Logged 25 Sept 2026, 21:07 UTC

The base rate heavily favors incumbent Susan Collins, but the only direct case-specific evidence — a September 14-15 Quantus poll showing Collins 48, Jackson 47 — is a near-tie, which dominates the incumbency prior and pulls the estimate toward 50-50.
Adjusting down from 50: Collins is a battle-tested incumbent who famously won in 2020 despite trailing in most polling, so a tied poll this late arguably understates her; Maine's polling has historically underestimated her support.
Adjusting up: Maine is a blue-leaning state in federal races, 2026 midterms typically favor the party out of the White House, and Jackson now has a clean nomination after the Platner withdrawal, consolidating Democratic support behind an establishment figure.
A single late-September poll within the margin of error is an anchor, not a distribution; the residual uncertainty over the remaining 38 days keeps the estimate well short of either extreme.

What would change it: A post-September polling average showing Collins ahead by 5+ points, or reporting that ranked-choice or third-party dynamics are structurally advantaging Collins, would push this estimate toward 0.30.

-12.5 probability points from the market at generation · med confidence · Polymarket

Base rate: U.S. Senate incumbents have won re-election roughly 85-90% of the time in recent cycles (e.g., ~84% in 2022, ~97% in 2024), so the base rate of the challenging party's nominee winning is about 10-15%; this rate comes from general knowledge of the class, as no historical Maine-specific win rate was retrievable.

Formed blind at 46.0%; published at 55.0% after the reconcile step moved it toward the market, stopping short on f3, f4. The market has likely absorbed the Sept 14–15 Quantus near-tie poll (f3), so the blind 46% gives Collins too little credit against the market's aggregate read; but the same tied poll (f3), plus Collins' documented history of outperforming Maine polling (f4), stops me short of the market's 67.5% since no retrieved fact explains why the race should price as a near two-thirds Democratic lock.

Chosen by hand.

What this call was reading

The September 14–15 Quantus Insights poll reported Susan Collins at 48% and Troy Jackson at 47%. as of 2026-09-15 · nytimes.com · within 39 days of this call
The contest is for Maine’s U.S. Senate seat, with Republican incumbent Susan Collins and Democratic nominee Troy Jackson as the two major-party candidates identified in the retrieved sources. as of 2026-09-23 · nytimes.com · within 39 days of this call
Maine Democrats selected Troy Jackson to replace Graham Platner as their Senate nominee after Platner withdrew. as of 2026-07-27 · maine.gov
The 2026 Maine U.S. Senate election has not yet occurred; the general election is scheduled for November 3, 2026. as of 2026-09-25 · fec.gov · within 39 days of this call
Maine’s 2026 U.S. Senate general election is scheduled for November 3, 2026. as of 2026-05-18 · fec.gov

Context

Materially different settlement terms. The venue readings below are not ranked as a comparable price gap.

Volume over the last 24 hours is active, at about $59,595 on the busier venue. It closes in 5 days. Prices this close to resolution move on news rather than on reassessment.

Related markets

Crossbook publishes every forecast it makes, timestamped before the answer is known and scored against the market afterwards. See the public record and the rules it is held to.

This call is line t-0216 of the public append-only ledger, committed when it was published. It appears on the record alongside every other call, resolved and open.