The Forecasting MachineOpen interactive report

Which party will win the 2026 US Senate election in New Hampshire?

The US Senate election in New Hampshire will be held on November 3, 2026. The incumbent, Jeanne Shaheen, is not seeking re-election. Key candidates include Chris Pappas (D) and John E. Sununu (R).

Forecasted on

Forecast probabilities

  • Democratic Party: 93.9%
  • Republican Party: 5.9%
  • Other Party / Independent: 0.2%

Reasoning

The evidence now points strongly to Chris Pappas: the late-summer dead heat gave way to a consistent run of polls showing him ahead, in a state and national environment that favor Democrats. The forecast is Democratic Party 93.9%, Republican Party 5.9%, and Other Party / Independent 0.2%—a clear favorite, not a certainty.

Democrats: A late polling advantage, reinforced by the broader climate

New Hampshire’s long record of electing Democrats to federal office gives Pappas a favorable starting point, though the state’s narrow presidential margin and willingness to elect Republican governors make it no safe harbor [a8, a1]. The most telling shift is in the polling: Sununu’s narrow August leads showed that the race could be close, but later surveys consistently moved the evidence in Pappas’s direction. Pappas led in the late-September New York Times/Siena poll, by seven points in the UMass Lowell/YouGov survey, and by six points in Rasmussen; Saint Anselm also found him ahead, including among independents. A poll reported on November 2 put Pappas ahead 54% to 42% [e1187] [e1105] [e1035] [e1034] [e1186].

Those polls are not isolated from the larger political setting. Late-October national surveys showed Democrats leading on the generic ballot, while Trump’s approval remained weak; forecasters also shifted their final ratings toward Democrats [e1193, e1194] [e1033] [e1195, e1196]. Pappas’s fundraising advantage—$23.7 million to Sununu’s $5.68 million—adds campaign capacity, and Kalshi classified the race as Safe Democratic [e1104] [e1077]. Ticket-splitting offers a useful local clue: among voters planning to split their tickets, most favored Republican Kelly Ayotte for governor and Pappas for Senate [e1148].

Republicans: A credible challenger, but a narrower path

Sununu is not an ordinary challenger. His former-senator status and family name give him recognition and crossover potential; Trump endorsed him, and August polling briefly showed him ahead or essentially tied with Pappas [e1189] [a4, a3]. Republicans also invested heavily: outside groups backed Sununu with advertising and voter-contact efforts, including AFP Action’s extensive canvassing [e1150] [e1072]. And the late polling cannot rule out a common error or a final shift toward Sununu.

But the later evidence is more numerous and points the other way. Sununu’s effort to distance himself from Trump suggests the national Republican brand may be a liability, while the Democratic lead widened nationally through the final stretch [e1079] [e1151]. His route to victory therefore depends on a polling miss, a late change in turnout, or both—not on the central tendency of the available evidence.

Other Party / Independent: Little evidence of a viable alternative

The contest is framed as a direct Pappas–Sununu race, and the polling and campaign activity described in the available evidence center on those two nominees [e1188] [e1032]. An independent or minor-party victory is possible in principle, but there is no sign of a credible third candidate with a realistic path to winning. That supports the very small 0.2% probability.

Why the probabilities are not closer

Forecasts should give more weight to a pattern of later, diverse polling than to an earlier stretch of tightening, while still leaving room for correlated polling error and Sununu’s candidate-specific strengths. Taken together, the final polling, Democratic-leaning national environment, Pappas’s fundraising edge, and the limited evidence for a third-party contender justify 93.9% for the Democratic Party, 5.9% for the Republican Party, and 0.2% for Other Party / Independent.

Update summary

A new poll put Pappas ahead 54% to 42%, reinforcing the late polling advantage already reflected in the forecast [e1186]. Late national polls and final ratings also moved in Democrats’ direction, while Election Day drew closer [e1193, e1194, e1195].

Cited evidence