Idaho · Senate

Who is running?

Jim Risch (Republican), Matt Loesby (Libertarian), Natalie M Fleming (Independent), Todd Achilles (Independent). The margin below is Todd Achilles minus the other candidate in the main contest; the rest are on the ballot and not in it.

The race, in brief

Idaho elects a senator on November 3, 2026. Republican incumbent Jim Risch is seeking a fourth term; the text notes Republicans have not lost a Senate race in the state since 1974, but gives no presidential results. The state profile on file gives a non-Hispanic white share of 0.8 and a median age of 37.1.

Risch won the May 19 primary with 67.3%. Realtor David Roth, the 2022 nominee, won the Democratic primary with 61.9%, but on July 8 the Ada County Democratic Central Committee gave him until August 12 to raise $50,000 or it would consider endorsing independent Todd Achilles, a former Democratic state representative who had entered with the support of Democratic leaders. Roth called the demands "completely ridiculous" and withdrew on July 28, leaving no Democratic nominee. Libertarian Matt Loesby and independent Natalie Fleming are also running. As of June 30, 2026 Risch had raised $4,431,093 with $3,535,956 on hand; Achilles $692,245 with $194,227.

All ten raters listed call the race R. The polls diverge: Advanced Targeting Research (September 13–16, 2026) had Achilles 50%, Risch 39%, and The Bullfinch Group (August 4–7) had Achilles 38%, Risch 33%, while Peak Insights, a Republican firm (August 11–13), had Risch 52%, Achilles 18%. Aggregates range from Risch +1.4 (Race to the WH) to Risch +18.9 (Silver Bulletin).

A paragraph quoting a model forecast from the day this brief was written is omitted; the current forecast is at the top of this page.

The facts, each beside its sentence

Not in the source: No Democratic nominee after Roth's withdrawal; the text does not say whether Democrats formally endorsed Achilles.; No presidential results for Idaho in the text.; Poll tables are rendered without clear column alignment; the Advanced Targeting and Bullfinch figures are read in column order.; The facts list Jim Risch with incumbent: false, while the text calls him the incumbent.; The facts give no forecast basis, so it is not known whether the model uses the statewide polls in the text.

Read from the district's section of Wikipedia's state page (CC BY-SA), archived as 549e4dd86ca6; written by claude-fable-5-1 (batch reader) on 2026-09-30 and checked mechanically: every quote occurs verbatim in the archived text, every number in the brief occurs in the inputs. No probability here is the reader's.

Who holds the seat now

James E. Risch (Republican), in this chamber since 2009, 3 terms, class 2 (term ends 2027). Committees: Senate Committee on Energy and Natural Resources; Senate Committee on Foreign Relations (Chairman); Senate Committee on Small Business and Entrepreneurship; Senate Select Committee on Ethics; Senate Select Committee on Intelligence; United States Senate Caucus on International Narcotics Control.

Mike Crapo (Republican), in this chamber since 1999, 5 terms, class 3 (term ends 2029). Committees: Senate Committee on Banking, Housing, and Urban Affairs; Senate Committee on Finance (Chairman); Senate Committee on the Budget; Joint Committee on Taxation (Chairman).

From the congress-legislators dataset (CC0), archived as ae8cb9477c48. For a Senate race this lists both of the state's senators; the one whose term ends in the election year holds the seat on the ballot. For a House district redrawn for 2026 it is the member elected under the old lines with this number, who may be running elsewhere; the dossier above names who is running here.

The money

FEC bulk candidate summaries through June 30, 2026; no independent expenditures reported for or against any candidate, which usually means nobody outside the district thinks it is in play.

How it has voted for president

A shift of 0.9 points toward the Republicans from 2016 to 2024. county returns summed; MEDSL county file (2016), an MIT-licensed county file (2020, checked against certified state results) and MEDSL precinct returns (2024). For a district split across counties this is an estimate, and where the state published the exact 2024 figure for these lines, that exact figure is the one the model uses.

The state in numbers

ACS 5-year state tables; BLS county unemployment and BEA county income, transfers and jobs summed to the state. Every figure is a named column of a named public-domain table, archived before it was read.

Who is ahead, and by how much?

Two numbers because they answer two questions. The nowcast is where opinion stands; the election-day forecast is where it is likely to end up.

How likely is each to win?

Monte Carlo error is ±0.1 points. A change smaller than that is simulation noise rather than news, and this page will not describe it as movement.

How wide is the range?

Nowcast: 90% of simulations fall between -33.0 and -1.2 points. Election day: -34.2 to +0.1. The election-day interval is 2.4 points wider, which is the 33 days of movement still to come.

What is the uncertainty made of?

Total sd 10.60 points, made of latent opinion 58%, race-specific polling error 22%, drift to election day 14%, correlated polling error 5%. The decomposition is stored with the forecast rather than reconstructed, so a probability whose dominant input is a placeholder is visibly that.

What evidence is this built on?

7 polls, most recent 2026-09-16. 25% verified against a primary source.

What changed since the last run?

Shaded band is the 90% interval, line is the central estimate, positive is Todd Achilles ahead of Jim Risch. Over 16 stored forecasts the central estimate moved -8.0 points. There were 7 specification changes (marked on the axis) and no new polls arrived over this window — so every movement in this chart is a change to the model, not a change in the race.

Since 2026-10-01: margin +0.00 points, win probability +0.0 points, on +0 polls. Of that, +0.00 points came from +0 poll(s), -0.00 from the shorter horizon, and +0.00 from the model specification.

How has this model done before?

Measured on 230 forecasts across 230 races in cycles 2016,2018,2020,2022,2024: mean absolute error 4.56 points, Brier score 0.0543. The nominal 90% interval contained the result 94% of the time, the 80% interval 84%, and the 50% interval 47%. Read that with care: a national polling miss moves every race in a cycle at once, so the sample size for a question about the intervals is 5 cycle(s), not 230 forecasts. Per cycle -- bias +1.644 pts; 2016: n=43 bias=+4.68 cov90=0.860; 2018: n=63 bias=-0.52 cov90=1.000; 2020: n=35 bias=+5.44 cov90=0.886; 2022: n=54 bias=-0.60 cov90=0.944; 2024: n=35 bias=+1.48 cov90=1.000.

Where did every number come from?

Nowcast run 5387ce44-e466-442e-8c69-4667dffe319a and election-day run e4e95f38-779c-4ac2-9db3-9c29af660d33, model single_race_latent/0.8.1 at commit bdf7e83107c17a2399efe61a44ef1bbee48f9284, seeds 20260924 and 20260924.