SD · Senate 2026 · Updated Oct 28, 2026, 2:01 a.m. ET
South Dakota
Rated Solid R
Mike Rounds wins this seat in 97 in 100 simulations. Call it all but certain.
Mike RoundsRIncumbent97 in 100- Brian BengsI3 in 100
Over time
How the forecast has moved
The margin
How close it lands
Each simulation produces a final margin. The curve shows where those margins fall; the tinted areas on either side of even are the futures each party wins.
Under the hood
What's driving the number
The forecast blends a weighted poll average with a fundamentals model: the state's partisan lean, incumbency, the national environment, and fundraising. Positive points favor the Democratic side of the margin; negative favor the Republican side.
- Partisan leanR +14.2
- IncumbencyR +2.5
- National environmentD +4.7
- FundraisingR +0.7
- Fundamentals sayR +12.7
- The polls sayR +13.4
- Blended forecast marginR +13.2
The blend puts 76 percent of its weight on the polls and 24 percent on the fundamentals; polls take over as more arrive and election day nears.
The field
How other forecasters see this race
Ours isn't the only model on this race. Where another forecaster publishes a number — or we've copied one in by hand from a paywalled model — it appears here beside ours, dated, because models update on their own schedules. Forecasts disagree for knowable reasons: different poll filters, different weights on the fundamentals, different priors.
- Mike Rounds winsThis forecast97 in 100
- Mike Rounds winsRametta & Hare · as of Oct 27>99 in 100
No model is "right" before the votes are counted. How our number is made — and how it scored against 2012–2024 races — is on the methodology page.
The markets
What the betting markets say
Prediction markets put a price on this seat too: what people are paying for a contract that pays out if Mike Rounds wins, read as an implied probability. Shown for comparison only. This is not betting advice, and market prices never feed the model.
- Mike Rounds winsThis forecast97 in 100
- Mike Rounds winsKalshi95 in 100
- Mike Rounds winsPolymarket95 in 100
Market prices as of Oct 28, 2026, 2:00 a.m. ET
The evidence
The polls, as the model sees them
Every public poll of this race, with the weight the model gave it in the latest run. Weights reward recency, sample size, and pollster track record; the house adjustment corrects each pollster's habitual lean before averaging.
| Poll | Dates | Sample | D–R | Margin | House adj. | Weight |
|---|---|---|---|---|---|---|
| Emerson College | Oct 19–20 | 803 LV | 42–50 | R +8.0 | — | 42% |
| Quantus Insights (R) | Oct 17–19 | 633 LV | 37–57 | R +20.0 | — | 18% |
| Public Opinon Strategies (R) | Oct 12–16 | 500 LV | 37–54 | R +17.0 | — | 12% |
| Mason-Dixon Polling & Strategy | Oct 12–14 | 500 RV | 37–56 | R +19.0 | — | 17% |
| Concord Public Opinion Partners (D) | Oct 6–8 | 400 LV | 43–42 | D +1.0 | — | 5% |
| Zenith Research | Sep 24–27 | 500 LV | 38–44 | R +6.0 | — | 3% |
| Public Policy Polling (D) | Sep 8–9 | 629 RV | 42–45 | R +3.0 | — | <1% |
| Lake Research Partners (D) | Aug 26–30 | 500 LV | 51–44 | D +7.0 | — | <1% |
| Impact Research (D) | Aug 13–17 | 500 LV | 44–44 | Even | — | <1% |
| Public Opinion Strategies (R) | Jul 6–9 | 500 LV | 33–56 | R +23.0 | — | <1% |
| Public Policy Polling (D) | May 29–30 | 726 RV | 23–43 | R +20.0 | — | <1% |
| Public Policy Polling (D) | Feb 17–18 | 685 RV | 35–47 | R +12.0 | — | 0% |
| Public Policy Polling (D) | Nov 13–14 | 814 RV | 31–44 | R +13.0 | — | 0% |
| Public Policy Polling (D) | Jul 30–31 | 524 LV | 28–41 | R +13.0 | — | 0% |
How the weights, the blend, and the simulation work is spelled out on the methodology page.