Background

Susan Collins is a Republican U.S. Senator from Maine who has served since 1997. She has historically outperformed typical Republican candidates in Maine, positioning herself as a moderate in a state that leans Democratic overall.

A January 2025 political science paper titled "The Electoral Consequences of Ideological Persuasion: Evidence from a Within-Precinct Analysis of U.S. Elections" by Bonica, Rhee, and Studen examines how candidate ideology affects vote share. The paper finds that a standard deviation change in ideological midpoint between candidates results in an average vote share penalty of 0.6 percentage points, with the authors concluding that "gains associated with ideological moderation are relatively modest and likely secondary to turnout effects."

Matthew Yglesias has challenged this paper's conclusions, suggesting that moderates like Susan Collins consistently outperform their state's partisan baseline, contrary to the paper's findings that ideological moderation offers only modest electoral advantages.

Resolution Criteria

This market will resolve to YES if Susan Collins outperforms the Republican partisan baseline in Maine by any margin in the 2026 Senate election, supporting Yglesias's position that moderate candidates like Collins do gain significant electoral advantages from their ideological positioning.

The market will resolve to NO if Susan Collins underperforms relative to the Republican partisan baseline in Maine in the 2026 Senate election.

The market will resolve to N/A if Susan Collins does not run for re-election in 2026.

The partisan baseline will be calculated by averaging Republican performance across other major statewide races in Maine during the 2024 and 2026 election cycles (including presidential, gubernatorial, and other federal races as applicable)

Clarification: Methodology for "Republican Baseline"

To ensure the "Republican Partisan Baseline" is robust and not reliant on a single data point (the Governor's race), the baseline for 2026 will be calculated by averaging the Republican vote share across three distinct statewide aggregates.

The 2026 Republican Baseline will be the arithmetic mean of:

1. The Gubernatorial Vote: The percentage of the vote received by the Republican candidate for Governor of Maine.

2. The Aggregated U.S. House Vote: The total number of votes cast for Republican candidates in ME-01 and ME-02 combined, divided by the total votes cast in both races.

3. The Aggregated State Legislative Vote: The total popular vote cast for all Republican candidates for the Maine State Senate and Maine House of Representatives, divided by the total votes cast only in those districts where a Republican candidate appears on the ballot.

Resolution Calculation:

If Susan Collins' vote share in the 2026 U.S. Senate election exceeds this calculated percentage, the market resolves YES.

Only count voters who express a preference in the comparison being measured.

So:

• Downballot race: exclude people who left the race blank.

• RCV final round: exclude ballots that exhausted before choosing between the final two.

Example

Down-ballot: 40 / (50 + 40) = 44.4% Republican

Senate: 49 / (50 + 49) = 49.5% Collins

So Collins outperforms by about 5.1 points.

• Update 2026-07-07 (PST) (AI summary of creator comment): For races using Ranked Choice Voting (RCV) (including Collins' Senate race and any federal House races used in the baseline): the certified final RCV-round vote share will be used if the race goes to RCV, otherwise the normal certified vote share. For non-RCV races (governor, state legislature): the certified Republican vote share as reported will be used.

• Update 2026-07-07 (PST) (AI summary of creator comment): When calculating the Republican baseline and Collins' vote share, blank/undervoted ballots are excluded from the vote share calculation (consistent with how exhausted ballots are excluded in RCV final tallies). The 2024 election results will not be used for the baseline; only 2026 statewide races will be used.