Skip to content
535

South Dakota Senate

  • Mike Rounds (Rep · incumbent)
  • Brian Bengs (Ind)

Favors Rep

Republicans99%

Republicans are favored, winning 98,922 of 100,000 simulated elections.

Favors Rep

Republicans100%

Republicans are favored, winning 99,981 of 100,000 simulated elections.

Forecast detail

as of Oct 4, 2026, 2:30 AM EDT

Estimated margin

R+22.5

5th–95th interval

R+38.5 to R+6.4

Estimated margin

R+19.8

5th–95th interval

R+28.9 to R+10.8

Win probability over time

Dem win probability Rep win probability Other win probability Tossup band

Polls

Ind-leaning poll Rep-leaning poll current average: R+5.3

Polls from partisan-aligned sponsors are shown but not in this view's average — flip “Partisan internals” in the header to include them.Partisan-sponsored polls are in this view's average, shifted 0.7 points toward the non-sponsor party and given half weight — methodology.

Pollster Dates Sample Results Margin House adj. Source
Brian Bengs (I) vs Mike Rounds (R) · 8 polls
Zenith Research ind sponsor Sep 24–Sep 27, 2026 500 lv Mike Rounds 53.0% Brian Bengs 47.0% R+6.0 — Source
Public Policy Polling ind sponsor Sep 8–Sep 9, 2026 629 rv Mike Rounds 45.0% Brian Bengs 42.0% R+3.0 R+1.5 R+1.5 lean removed Source
Impact Research ind sponsor Aug 13–Aug 17, 2026 500 lv Mike Rounds 44.0% Brian Bengs 44.0% Even — Source
Public Opinion Strategies rep sponsor Jul 6–Jul 9, 2026 500 lv Mike Rounds 56.0% Brian Bengs 33.0% R+23.0 — Source
Public Policy Polling ind sponsor May 29–May 30, 2026 726 rv Mike Rounds 44.0% Brian Bengs 40.0% R+4.0 R+2.5 R+1.5 lean removed Source
Public Policy Polling ind sponsor Feb 17–Feb 18, 2026 685 rv Mike Rounds 47.0% Brian Bengs 35.0% R+12.0 R+10.5 R+1.5 lean removed Source
Public Policy Polling ind sponsor Nov 13–Nov 14, 2025 814 rv Mike Rounds 44.0% Brian Bengs 31.0% R+13.0 R+11.5 R+1.5 lean removed Source
Public Policy Polling ind sponsor Jul 30–Jul 31, 2025 552 rv Mike Rounds 41.0% Brian Bengs 28.0% R+13.0 R+11.5 R+1.5 lean removed Source
Brian L. Bengs (I) vs Julian Beaudion (D) · 1 poll
Public Policy Polling ind sponsor May 29–May 30, 2026 726 rv Brian Bengs 56.0% Dem 31.0% — — Source
Brian L. Bengs (I) vs Julian Beaudion (D) vs Mike Rounds (R) · 1 poll
Public Policy Polling ind sponsor May 29–May 30, 2026 726 rv Mike Rounds 43.0% Brian Bengs 23.0% Dem 18.0% R+20.0 R+18.5 R+1.5 lean removed Source
Julian Beaudion (D) vs Mike Rounds (R) · 2 polls
Public Policy Polling ind sponsor Feb 17–Feb 18, 2026 685 rv Mike Rounds 49.0% Dem 32.0% — — Source
Public Policy Polling ind sponsor Nov 13–Nov 14, 2025 814 rv Mike Rounds 52.0% Dem 30.0% — — Source

Dispatches about this race

Poll reaction South Dakota Senate Sep 30, 2026

Zenith poll puts Rounds ahead of Bengs, and our South Dakota forecast holds

The new survey's 53-47 result lands near the narrow edge of our simulated range, and our odds and margin are identical to the previous run.

A Zenith Research survey of 500 likely voters in South Dakota, fielded September 24-27, has Republican Sen. Mike Rounds at 53% and independent Brian Bengs at 47%.

Our forecast did not change with it. Our model gives Rounds a 99 in 100 chance of winning the seat and Bengs a 1% chance. Our...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5.5

Poll reaction South Dakota Senate Sep 11, 2026

Another close South Dakota poll, and our numbers do not move

A Public Policy Polling survey puts Mike Rounds three points from Brian Bengs, while our model still has the race at R+24 and the Republican at 99 percent.

A Public Policy Polling survey of 629 registered voters in South Dakota, fielded September 8-9, had Republican incumbent Mike Rounds at 45 percent and independent Brian Bengs at 42 percent. The poll does not report a margin of error, and a three-point gap in a sample that size is close.

Our...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5

Poll reaction South Dakota Senate Aug 31, 2026

Our South Dakota margin widens again while the odds stay put

A tied August poll and two much older ones leave Mike Rounds at a 98 percent chance in our model, with a far wider range of outcomes than in the prior run.

The most recent survey of the South Dakota Senate race has it even. Impact Research polled 500 likely voters August 13-17 and found Republican incumbent Mike Rounds at 44 percent and independent Brian Bengs at 44 percent.

The other numbers in front of us are older and point the other way. Public...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5

Poll reaction South Dakota Senate Aug 28, 2026

A tied poll in South Dakota narrows our margin, not the odds

Impact Research finds Mike Rounds and independent Brian Bengs level at 44, while our model still gives Rounds an effectively certain win.

An Impact Research survey of 500 likely voters in South Dakota, fielded August 13-17, put Republican incumbent Mike Rounds and independent Brian Bengs level at 44 percent each.

Our model absorbed the number and moved, but not far. Our current estimate of the margin is R+19.6, with a...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5