SD · Senate 2026 · Updated Aug 27, 2026, 2:03 a.m. ET
South Dakota
Rated Likely R
Mike Rounds wins this seat in 92 in 100 simulations. Call it clearly favored.
Mike RoundsRIncumbent92 in 100- Brian BengsI8 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 +5.1
- FundraisingR +1.1
- Fundamentals sayR +12.8
- The polls sayR +25.5
- Blended forecast marginR +13.0
The blend puts 2 percent of its weight on the polls and 98 percent on the fundamentals; polls take over as more arrive and election day nears.
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 forecast92 in 100
- Mike Rounds winsKalshi95 in 100
- Mike Rounds winsPolymarket96 in 100
Market prices as of Aug 27, 2026, 2:03 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 |
|---|---|---|---|---|---|---|
| Public Opinion Strategies (R) | Jul 6–9 | 500 LV | 33–56 | R +23.0 | — | 94% |
| Public Policy Polling (I) | May 29–30 | 726 RV | 23–43 | R +20.0 | — | 6% |
| Public Policy Polling (I) | Feb 17–18 | 685 RV | 35–47 | R +12.0 | — | <1% |
| Public Policy Polling (I) | Nov 13–14 | 814 RV | 31–44 | R +13.0 | — | 0% |
| Public Policy Polling (I) | 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.