South Dakota · Senate
election 2026-11-03 · forecast as of 2026-10-01 · margins and probabilities are for Brian Bengs
Who is running?
Mike Rounds (Republican), Brian Bengs (Independent). The margin below is Brian Bengs minus the other candidate in the main contest; the rest are on the ballot and not in it.
The race, in brief
South Dakota elects a U.S. senator on November 3, 2026. The state profile on file records a non-Hispanic white share of 0.8, a college share of 0.311 and a median age of 37.7. The text notes that Republicans have not lost a Senate election in the state since 2008.
Republican incumbent Mike Rounds, a senator since 2015, is seeking a third term. He won the June 2 primary with 75.8% over Justin McNeal. The Democratic nominee, former state trooper Julian Beaudion, won unopposed but withdrew on August 4, so the main challenger is independent Brian Bengs, a Navy and Air Force veteran, former Northern State University professor and the 2022 Democratic nominee. In the latest filings Rounds had raised $4,513,920 with $2,736,663 on hand, Bengs $782,049 with $51,405 on hand.
All ten raters listed, from the Cook Political Report to Split Ticket, rate the race R, with dates between September 17 and September 30, 2026. The polling is closer: the Silver Bulletin aggregate through September 9 has Rounds 48.2% to Bengs 45.0%. Public Policy Polling (D), September 8–9, had Rounds 45%, Bengs 42%; Impact Research (D), August 13–17, had them tied at 44%; Public Opinion Strategies (R), July 6–9, had Rounds 56%, Bengs 33%.
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
Republican incumbent Mike Rounds is seeking a third term.
Republican incumbent Mike Rounds is seeking a third term.
Former state trooper Julian Beaudion won Democratic nomination unopposed, but withdrew from the race on August 4.
Mike Rounds, incumbent U.S. senator (2015–present)
Mike Rounds, incumbent U.S. senator (2015–present)
Primary elections were held on June 2. Rounds received 75.8% of the vote against minimal opposition.
The Cook Political Report R September 23, 2026 Decision Desk HQ R September 25, 2026
Mike Rounds (R)As of June 2, 2026 $4,513,920 $3,459,778 $2,736,663
Brian Bengs, U.S. Navy and Air Force veteran, former Northern State University political science professor, and Democratic nominee for U.S. Senate in 2022
Silver Bulletin through September 9, 2026 September 14, 2026 |48.2% 45.0% 6.8% |Rounds +3.2%
Public Policy Polling (D) September 8–9, 2026 629 (RV) ±3.6% |45% 42% 13%
Impact Research (D) August 13–17, 2026 500 (LV) ±4.4% 44% 44% 12%
Public Opinion Strategies (R) July 6–9, 2026 500 (LV) ±4.4% |56% 33% 11%
Republicans have not lost a Senate election in South Dakota since 2008.
Not in the source: facts.forecast carries no basis field, so the dossier cannot say whether the model uses the state polls reported here.; facts.candidates marks Rounds as incumbent: false, while the text names him the Republican incumbent.; The text does not say whether Democrats named a replacement for Beaudion or whether his name remains on the ballot.; Ratings are given only as 'R', with no Safe/Likely/Lean grade.; No endorsements are listed (the endorsement sections are empty in the text).
Read from the district's section of Wikipedia's state page (CC BY-SA), archived as 138b809d1547; 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
John Thune (Republican), in this chamber since 2005, 4 terms, class 3 (term ends 2029). Committees: Senate Committee on Agriculture, Nutrition, and Forestry; Senate Committee on Commerce, Science, and Transportation; Senate Committee on Finance; Senate Select Committee on Intelligence (Ex Officio).
Mike Rounds (Republican), in this chamber since 2015, 2 terms, class 2 (term ends 2027). Committees: Senate Committee on Appropriations; Senate Committee on Armed Services; Senate Committee on Banking, Housing, and Urban Affairs; Senate Committee on Indian Affairs; Senate Select Committee on Intelligence; Commission on Security and Cooperation in Europe.
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
| Candidate | Raised | Cash on hand | PAC share | Self-funded | Outside $ for | Outside $ against |
|---|---|---|---|---|---|---|
| Rounds, Mike (REP) incumbent | $3,176,451 | $2,736,664 | 44% | 0% | $565,848 | $0 |
| Bengs, Brian (IND) challenger | $782,050 | $51,406 | 1% | 0% | $0 | $0 |
| Beaudion, Julian C (DEM) challenger · not on our roster | $228,295 | $3,078 | 1% | 2% | $0 | $0 |
| Mcneal, Justin S (REP) challenger · not on our roster | $10,993 | $1 | 0% | 1% | $0 | $0 |
FEC bulk candidate summaries through June 30, 2026; $565,848 of independent expenditures for or against these candidates this cycle (FEC Schedule E, types 24E and 24A), which is the parties' and outside groups' own revealed view of whether this seat is in play.
How it has voted for president
| Two-party margin | 2016 | 2020 | 2024 |
|---|---|---|---|
| President | R+31.9 | R+26.9 | R+29.9 |
A shift of 2.1 points toward the Democrats 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
| Measure | State | Average state | Difference |
|---|---|---|---|
| Bachelor's degree or higher, 25+, 2023 | 31.1% | 34.0% | -2.9 pts |
| White, non-Hispanic, 2023 | 80.3% | 66.3% | +14.0 pts |
| Black, non-Hispanic, 2023 | 2.2% | 10.1% | -7.9 pts |
| Hispanic or Latino, 2023 | 4.6% | 12.9% | -8.3 pts |
| Asian, non-Hispanic, 2023 | 1.4% | 4.4% | -3.0 pts |
| Foreign-born, 2023 | 3.9% | 9.6% | -5.7 pts |
| Median age, 2023 | 37.7 | 39.1 | -1.38 |
| Median household income, 2023 | $72,421 | $77,633 | $-5,212 |
| Median home value, 2023 | $236,800 | $314,132 | $-77,332 |
| Owner-occupied homes, 2023 | 68.6% | 67.4% | +1.3 pts |
| Unemployment (ACS), 2023 | 3.0% | 4.8% | -1.8 pts |
| Federal government workers, 2023 | 3.2% | 3.0% | +0.2 pts |
| Work from home, 2023 | 9.3% | 12.3% | -3.0 pts |
| Households on SNAP, 2023 | 8.1% | 11.1% | -3.0 pts |
| Households with Social Security income, 2023 | 31.1% | 32.1% | -1.0 pts |
| Households with public assistance income, 2023 | 2.1% | 2.6% | -0.5 pts |
| Moved in from another state, past year, 2023 | 3.2% | 2.9% | +0.4 pts |
| Gini index, 2023 | 0.45 | 0.47 | -0.02 |
| Unemployment, latest month (BLS), 2026-07 | 2.0% | 4.0% | -2.0 pts |
| Change in unemployment, past 12 months, 2026-07 | +0.1 pts | -0.1 pts | +0.2 pts |
| Change since the last election (24 months), 2026-07 | +0.2 pts | -0.1 pts | +0.3 pts |
| Per-capita personal income (BEA), 2024 | $75,699 | $70,662 | $+5,037 |
| Per-capita income growth since 2019, nominal, 2024 | 39.1% | 32.4% | +6.8 pts |
| Government and other transfers, share of income, 2024 | 17.0% | 19.4% | -2.4 pts |
| Social Security, share of income, 2022 | 5.5% | 6.1% | -0.6 pts |
| Medicare, share of income, 2022 | 3.8% | 4.4% | -0.6 pts |
| Medicaid, share of income, 2022 | 2.1% | 3.8% | -1.7 pts |
| SNAP, share of income, 2022 | 0.3% | 0.6% | -0.3 pts |
| Earned Income Tax Credit, share of income, 2022 | 0.2% | 0.3% | -0.1 pts |
| Veterans' benefits, share of income, 2022 | 0.9% | 0.9% | +0.0 pts |
| Federal civilian jobs, share of all jobs, 2022 | 1.7% | 1.5% | +0.2 pts |
| Military jobs, share of all jobs, 2022 | 1.2% | 1.2% | +0.1 pts |
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 -20.0 and +0.5 points. Election day: -21.7 to +2.3. The election-day interval is 3.6 points wider, which is the 33 days of movement still to come.
What is the uncertainty made of?
Total sd 7.60 points, made of race-specific polling error 43%, drift to election day 28%, latent opinion 19%, correlated polling error 10%. 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?
8 polls, most recent 2026-09-27. 44% verified against a primary source.
What changed since the last run?
Shaded band is the 90% interval, line is the central estimate, positive is Brian Bengs ahead of Mike Rounds. Over 16 stored forecasts the central estimate moved -2.0 points. There were 7 specification changes (marked on the axis) and 1 new poll arrived over this window — so the movement mixes new evidence with changes to the model.
Since 2026-10-01: margin +0.00 points, win probability +0.0 points, on +0 polls.
Not answered here: why it changed. Splitting a move into new polls, time and specification means re-running the earlier model against the later inputs -- two extra posterior fits -- so it is computed on a cadence (scripts/attribute_forecasts.py) rather than while you wait. This pair of runs has not been decomposed yet. The size of the move is shown; the cause is not guessed at.
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 5f86327d-0bf5-4524-a745-1f665b853515 and election-day run a0564ecf-e2fd-4058-8a23-f76494fff6e7, model single_race_latent/0.8.1 at commit bdf7e83107c17a2399efe61a44ef1bbee48f9284, seeds 20260924 and 20260924.