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FORECAST51 DAYS OUT
← Senate3 November 2026 · 51 days out

South Dakota · U.S. Senate

Open this race on The Map ↗

Mike Rounds is heavily favored to win. Projected candidate margin: Mike Rounds over Brian Bengs by 15.0 points. No two-party forecast is published for this race: this race is between an independent and a major-party candidate, so the forecast is published per candidate rather than as a two-party margin.

Mike Rounds (R)97 in 10097.2%57.4high 62.5 · low 52.3
Brian Bengs (I)3 in 1002.8%42.4high 47.5 · low 37.3
Other (minor parties / write-ins)—0.2high 0.4 · low 0.0
Field notes

Official ballot sources: Brian Bengs (checked 2026-08-31).

high / low: vote share (%) in the middle 80 in 100 simulations

About this field

Not competitive.

Forecast share averages the simulated vote. Win chance counts how often a candidate wins. A wider range of outcomes can give a candidate a higher win chance despite a lower average share.

Solid RRepublican-held seat

The polls

Ledger weighted average R+6.4Used by the forecast: 6 polls (60-day half-life) · measured R+5.6 · after the fitted poll-error shift R+7.17 recorded polls · 7 eligible for the aggregate · 7 with positive weight

FieldworkAddedPollsterResultSample
from 2026-09-082d agoPublic Policy Polling ↗R+3.0I 42% · R 45%629 RV
from 2026-08-13Impact Research ↗EVENI 44% · R 44%500 LV
from 2026-07-06Public Opinion Strategies ↗National Republican Senatorial CommitteeR+23.0I 33% · R 56%500 LV
from 2026-05-29Public Policy Polling ↗R+20.0I 23% · R 43%726 RV
from 2026-02-17Public Policy Polling ↗R+12.0I 35% · R 47%685 RV
from 2025-11-13Public Policy Polling ↗R+13.0I 31% · R 44%814 RV
from 2025-07-30Public Policy Polling ↗R+13.0I 28% · R 41%552 RV
Explore all 7 polls for this race

How the partisan coordinate was built

Follow each contribution to the margin. Wider ribbons mean more percentage points. Tap an input for its calculation and source.

Toward I+17.6
Toward R−32.5
Net coordinateR+15.0

The signed totals combine at the forecast. Displayed values are rounded. This is a modeled partisan coordinate.

Mike Rounds leads Brian Bengs by 15.0 points (candidate-pair center). The named candidate forecast also accounts for the field and election rules; its lead is a separate quantity from the partisan coordinate above.

All calculations & sources

How this state voted, 2024 −29.190 points

The state's two-party presidential margin in 2024, from our own county sums — the same measurement the model's statewide terrain center is built from. Every pull below is measured from here, not from EVEN, which is why a landslide seat's listed pulls are small numbers and still land where the forecast does.

  • 2024 presidential result for this state, two-party, from Call the Map's own county sums.
  • Same source as Act I's 2024-president reference mark, so the origin lands on it.

This race’s polls +11.965 points

What this race’s own recent polling adds beyond its prior, after each poll is weighted for recency, sample size and pollster quality.

  • 7 matchup-validated, sample/recency/grade-weighted poll(s), latest 2026-09-09
  • Public Policy Polling (2026-09-09, n=629): R+3.0 · weight 0.96
  • Impact Research (2026-08-17, n=500): ±0.0 · weight 0.40
  • Public Opinion Strategies (2026-07-09, n=500): R+23.0 · weight 0.11
  • Public Policy Polling (2026-05-30, n=726): R+20.0 · weight 0.04
  • Public Policy Polling (2026-02-18, n=685): R+12.0 · weight 0.00
  • Public Policy Polling (2025-11-14, n=814): R+13.0 · weight 0.00
  • … and 1 more below.
  • Adjusted poll-bank aggregate R+6.4 · 7 recorded polls · 7 eligible for the aggregate · 7 with positive weight. The sealed model records a net polling contribution of +12.0 D. Observation weights are not the final model blend weight. Eligible polls: latest poll: 2026-09-09 (4 days old).
  • Adjusted poll-bank aggregate R+6.4 · 7 recorded polls · 7 eligible for the aggregate · 7 with positive weight; recorded polling contribution +12.0 D. These observation weights must not be read as the model’s final prior-versus-polling weight. Eligible polls: latest poll: 2026-09-09 (4 days old).

Fitted model, above the terrain shown +3.612 points

What the fitted model adds on top of the starting terrain above — incumbency, past results, campaign finance and the other fitted terms — measured from that terrain rather than from EVEN. It is a comparison with the starting point already shown, not a separate input. The source detail lists the variables the fit uses.

  • Fitted baseline -25.578 minus starting point -29.190 = 3.612 points.
  • For orientation, the presidential results here: 2024 R+29.2, 2020 R+26.2.
  • The work: the −25.6 D fundamentals push is the sum of the dynamic formula's surviving variables for this race — each one's own contribution is listed below.
  • fundamentals core = 25-term dynamic formula (mass fit over the master feature matrix, held-out-cycle validated; see matrix/feature_dictionary.md + mass_fit_report.json)
  • 9-term formula, held-out validated.

National environment +1.988 points

The contribution to this race’s margin, not the national polling margin itself. The race’s loading, reference level and polling blend determine how much of the national climate reaches its final forecast.

  • Three-source blend, updated 2026-09-08: 52% generic-ballot aggregates (D+6.5) · 28% special-election overperformance (D+9.0 across 46 specials) · 20% approval-implied (D+8.6 from net approval -21.7).
  • Latest polls — generic ballot 2026-09-08 (5 days old), approval 2026-09-10 (3 days old).
  • Generic-ballot average D+6.5 · support factor 0.84 (the share of that channel's capacity the admitted polls carry) — separate inputs; their product is a capacity diagnostic, not a margin.
  • Weights are the 55/25/20 capacities scaled by each channel's evidence and renormalized, so thin polling widens the interval instead of pulling the center toward zero — 16% of the weight is carried that way.
  • Blended national environment: D+7.6.
  • Applied at full strength to this chamber's races.
  • The work: national environment × 1 chamber strength = +2.0 D of this margin.
  • Blended national environment: D+7.6 (updated 2026-09-08).
  • Effective poll weight 84%; fundamentals share 16%, carried by the interval (×1.08) rather than by the center.
  • The support factor is the share of the generic-ballot capacity the admitted polls carry; average × support is a capacity diagnostic, not a margin, and is not what the row above multiplies.
  • Applied at full strength to this chamber: +2.0 of this margin.

Structural safeguards −3.358 points

Bounded corrections that keep the model consistent with structural facts.

  • Applied only when a safe state's dynamic fundamentals point in the same direction as its strong presidential lean but are materially compressed toward zero.
  • The 25% correction toward that lean improved safe-race MAE in strict expanding-window validation without changing a historical call.
  • The disclosed adjustment is −3.4 D.

These are the fitted model’s named contributions to the partisan coordinate, before the candidate-field calculation.

Named factorContribution
FundamentalsThe admitted fitted baseline. Its surviving variables differ by office; the source detail above identifies those used for this race.−25.58
This race's pollsAdmitted head-to-head polls of this race, recency- and quality-weighted.+11.97
Structural terrain safeguardA bounded pull toward presidential terrain in heavily partisan states.−3.36
National environmentThe national environment’s contribution to the prior. Polling can attenuate its influence; this value is not the national polling margin.+1.99
Other factors−0.00

Recent elections

ElectionResultVotes cast
2020 · U.S. Senate ↗R+31.5420,219
2014 · U.S. Senate ↗R+26.1279,412
2008 · U.S. Senate ↗D+25.0380,673
2002 · U.S. Senate ↗D+0.2337,501

Margins compare Democratic and Republican vote totals. Nonstandard ballots are labeled separately.

The money

Bar length compares reported receipts in this race; the tick marks cash on hand. A missing filing stays blank rather than becoming $0.

One more fundraising reportCall the Map · $0

The candidates are comfortably out-fundraising the website covering them. A little rude, perhaps, but statistically unsurprising.

Received so far
$0
Measured compute
$26,188.58

Ko-fi and Buy Me a Coffee receipts are counted through Sep 1, 2026. Measured compute prices model runs at standard published API rates; it is not what I paid. Hosting, data and subscriptions, the domain and my own time are not counted. Donations buy gratitude, never a forecast adjustment.

Ko-fi ↗Buy Me a Coffee ↗

See the public support ledger →

Outside spending

Support + opposition · separate from receipts

For and against Brian Bengs$414K

1 spending group
GroupForAgainst
SOUTH DAKOTA CONSERVATIVE PAC$0$414K

For and against Mike Rounds$587K

2 spending groups
GroupForAgainst
DEFEND AMERICAN JOBS$412K$0
SOUTH DAKOTA CONSERVATIVE PAC$175K$0

Includes primary spending. Opposition is recorded against its named target; no benefit to another candidate is assumed.

FEC filings · through 06/30/2026 · Definitions & method

Race context

Forecast votes cast
340,397
Forecast turnout
49.6% of the voting-eligible population
2024 presidential margin
R+29.9

Statewide, 50.4% of the voting-eligible population is projected to cast a ballot; the lower figure above is the share projected to vote in this race.

Population profile Select a measure for its source and denominator

White alone · 82.2%731,624 of 890,342 · Residents2022 Census · matched race geography
Demographic source and limits

U.S. Census Bureau, 2022 American Community Survey 5-year estimates ↗

Coverage

1 quote

All coverage and full posts on the Wire →