Senate · 2026

South Dakota Senate

Brian Bengs (I)v.Mike Rounds (R)LIKELY R

Incumbent: Mike Rounds, currently Republican. No Democratic nominee: Brian Bengs (independent) stands on the Democratic side of the margin. The projection is the polling average alone, with a wider interval, because no independent-versus-Republican race is in the backtest.

Projected margin

R+8.0

Nine in ten outcomes: I+3 to R+19

Chance of winning

87%

Mike Rounds

Polls alone

R+8.0

6 polls from 3 pollsters; latest Sep 9. Weight in projection: 100%.

Fundamentals alone

R+22.9

Weight in projection: 0%.

Polls

The average over time

Each poll is first shifted by its sponsor's and its pollster's measured lean, then weighted by recency and track record. Sample size gets no weight: in 2,000-plus past races it predicted nothing about accuracy. Why.

adjusted weighted average shading: which side the average favors each poll, as published party-aligned pollster or sponsor

Before any poll

What the fundamentals say

A regression on past Senate races, fit without looking at this year. The national environment term uses the generic ballot after its historical correction (D+5.3).

What each term adds to the estimate

BaselineI+0.5

Partisan leanR+20.6

National environmentI+3.3

IncumbencyR+1.8

Incumbent's last over/under-performanceR+2.1

Fundraising gapR+2.2

Fundamentals estimateR+22.9

Input: partisan lean

R+27.7

Presidential vote relative to the nation, 2024 (and 2020).

Input: raised from itemized individual donors, through June 30

$315K I · $1.1M R

FEC filings; the model uses the log of the ratio.

Handicappers, for comparison

Cook: Safe R · Sabato: Safe R · Inside Elections: Safe R

Not an input to the projection.

Table view

All 6 polls in the average

“Share” is how much of today’s average each poll supplies. It depends on recency, the pollster’s record, whether the poll screens for likely voters, and how many other polls the same firm has in the race. It does not depend on sample size.

Dates	Pollster	Sample	Bengs	Rounds	As published	Adjusted	Share of average
Sep 8–9	Public Policy PollingDEM.-ALIGNED for Bengs' campaign	629 RV	42	45	R+3	R+6.5 moved 3.5 toward R	33%	source
Aug 13–17	Impact ResearchDEM.-ALIGNED for Bengs' campaign	500 LV	44	44	Even	R+3.7 moved 3.7 toward R	41%	source
Jul 6–9	Public Opinion StrategiesREP.-ALIGNED for National Republican Senatorial Committee	500 LV	33	56	R+23	R+19.0 moved 4.0 toward I	20%	source
May 29–30	Public Policy PollingDEM.-ALIGNED for Bengs' campaign	726 RV	40	44	R+4	R+7.5 moved 3.5 toward R	4.8%	source
Feb 17–18	Public Policy PollingDEM.-ALIGNED for Bengs' campaign	685 RV	35	47	R+12	R+15.5 moved 3.5 toward R	0.7%	source
Nov 13–14 ’25	Public Policy PollingDEM.-ALIGNED for Bengs' campaign	814 RV	31	44	R+13	R+16.5 moved 3.5 toward R	0.1%	source

LV: likely voters. RV: registered voters. A: all adults. “Adjusted” is the published margin after removing the sponsor shift and the pollster’s measured house effect; the small print says how far that moved the poll. Dem.-aligned and Rep.-aligned mark polls paid for by a party, a campaign, or an allied group, or taken by a firm whose published work is mostly for one side. They are shifted by the average lean of such polls, then counted at full weight.

History

Recent results for this office

Year	Democrat	Republican	Result
2022	Brian L. Bengs	John R. Thune	R+43.5
2020	Daniel P. Ahlers	M. Michael Rounds	R+31.5
2016	Jay H. Williams	John R. Thune	R+43.7
2014	Richard P. Weiland	M. Michael Rounds	R+20.9