South Dakota · U.S. Senate
Mike Rounds is almost certain to win. Projected candidate margin: Mike Rounds over Brian Bengs by 15.2 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.
Field notes
Official ballot sources: Brian Bengs (checked 2026-08-31).
Under each share, its likely range (80 in 100 simulations) · * incumbent
Background
Not competitive.
Forecast history
Latest reading · Oct 28 · first published Oct 6 · Lead between the top two candidates, in points of all votes. Methodology
About this series
Reconstructed with the current model Aug 1 – Oct 5; published readings Oct 6 – Oct 28. Each reconstructed day is the current model on that day’s own inputs, not a forecast published then. Corrections are dated in the changelog.
Faded: CTMM 2.2 reconstructed history: computed after the fact with each date's available polls and environment, without expert ratings; not an issued forecast. Issued forecasts begin at the launch marker.
CTMM 2.2 readings for 2026-09-16, 2026-09-17, 2026-09-18 were computed after the fact with each day's available inputs: no edition was issued on those days. Not an issued forecast.
Data table
| Date | Lead | Chance | Reading |
|---|---|---|---|
| Oct 28 | R+15.2 | Mike Rounds win 98.9% | Published forecast |
| Oct 27 | R+15.2 | Mike Rounds win 98.9% | Published forecast |
| Oct 26 | R+16.3 | Mike Rounds win 99.3% | Published forecast |
| Oct 25 | R+15.2 | Mike Rounds win 98.9% | Published forecast |
| Oct 24 | R+15.2 | Mike Rounds win 98.9% | Published forecast |
| Oct 23 | R+15.2 | Mike Rounds win 99.0% | Published forecast |
| Oct 22 | R+14.4 | Mike Rounds win 98.0% | Published forecast |
| Oct 21 | R+9.0 | Mike Rounds win 89.4% | Published forecast |
| Oct 20 | R+9.0 | Mike Rounds win 89.6% | Published forecast |
| Oct 19 | R+8.4 | Mike Rounds win 87.8% | Published forecast |
| Oct 18 | R+8.5 | Mike Rounds win 87.9% | Published forecast |
| Oct 17 | R+8.5 | Mike Rounds win 88.0% | Published forecast |
| Oct 16 | R+9.0 | Mike Rounds win 89.1% | Published forecast |
| Oct 15 | R+9.3 | Mike Rounds win 89.7% | Published forecast |
| Oct 14 | R+9.3 | Mike Rounds win 89.8% | Published forecast |
| Oct 13 | R+9.3 | Mike Rounds win 89.9% | Published forecast |
| Oct 12 | R+9.4 | Mike Rounds win 90.1% | Published forecast |
| Oct 11 | R+9.4 | Mike Rounds win 90.1% | Published forecast |
| Oct 10 | R+9.4 | Mike Rounds win 90.2% | Published forecast |
| Oct 9 | R+9.4 | Mike Rounds win 90.3% | Published forecast |
| Oct 8 | R+9.5 | Mike Rounds win 90.4% | Published forecast |
| Oct 7 | R+9.5 | Mike Rounds win 90.5% | Published forecast |
| Oct 6 | R+9.6 | Mike Rounds win 90.7% | Published forecast |
| Oct 5 | R+9.6 | Mike Rounds win 90.8% | Recomputed with the current model |
| Oct 4 | R+9.6 | Mike Rounds win 90.9% | Recomputed with the current model |
| Oct 3 | R+9.6 | Mike Rounds win 91.0% | Recomputed with the current model |
| Oct 2 | R+9.7 | Mike Rounds win 91.1% | Recomputed with the current model |
| Oct 1 | R+10.5 | Mike Rounds win 92.5% | Recomputed with the current model |
| Sep 30 | R+10.5 | Mike Rounds win 92.5% | Recomputed with the current model |
| Sep 29 | R+11.2 | Mike Rounds win 92.1% | Recomputed with the current model |
| Sep 28 | R+11.3 | Mike Rounds win 92.2% | Recomputed with the current model |
| Sep 27 | R+11.3 | Mike Rounds win 92.2% | Recomputed with the current model |
| Sep 26 | R+11.3 | Mike Rounds win 92.3% | Recomputed with the current model |
| Sep 25 | R+11.3 | Mike Rounds win 92.3% | Recomputed with the current model |
| Sep 24 | R+11.4 | Mike Rounds win 92.4% | Recomputed with the current model |
| Sep 23 | R+11.4 | Mike Rounds win 92.5% | Recomputed with the current model |
| Sep 22 | R+11.4 | Mike Rounds win 92.6% | Recomputed with the current model |
| Sep 21 | R+11.5 | Mike Rounds win 92.6% | Recomputed with the current model |
| Sep 20 | R+11.5 | Mike Rounds win 92.7% | Recomputed with the current model |
| Sep 19 | R+11.5 | Mike Rounds win 92.8% | Recomputed with the current model |
| Sep 18 | R+11.5 | Mike Rounds win 92.7% | Reconstructed with the stated inputs |
| Sep 17 | R+11.5 | Mike Rounds win 92.8% | Reconstructed with the stated inputs |
| Sep 16 | R+11.5 | Mike Rounds win 92.9% | Reconstructed with the stated inputs |
| Sep 15 | R+11.6 | Mike Rounds win 93.1% | Recomputed with the current model |
| Sep 14 | R+11.7 | Mike Rounds win 93.1% | Recomputed with the current model |
| Sep 13 | R+11.7 | Mike Rounds win 93.2% | Recomputed with the current model |
| Sep 12 | R+11.7 | Mike Rounds win 93.3% | Recomputed with the current model |
| Sep 11 | R+11.7 | Mike Rounds win 93.4% | Recomputed with the current model |
| Sep 10 | R+14.3 | Mike Rounds win 95.1% | Recomputed with the current model |
| Sep 9 | R+14.3 | Mike Rounds win 95.2% | Recomputed with the current model |
| Sep 8 | R+14.3 | Mike Rounds win 95.2% | Reconstructed with the stated inputs |
| Sep 7 | R+14.4 | Mike Rounds win 95.3% | Reconstructed with the stated inputs |
| Sep 6 | R+14.4 | Mike Rounds win 95.3% | Reconstructed with the stated inputs |
| Sep 5 | R+14.5 | Mike Rounds win 95.4% | Reconstructed with the stated inputs |
| Sep 4 | R+14.5 | Mike Rounds win 95.5% | Reconstructed with the stated inputs |
| Sep 3 | R+14.5 | Mike Rounds win 95.5% | Reconstructed with the stated inputs |
| Sep 2 | R+14.5 | Mike Rounds win 95.5% | Reconstructed with the stated inputs |
| Sep 1 | R+13.6 | Mike Rounds win 95.3% | Reconstructed with the stated inputs |
| Aug 31 | R+13.6 | Mike Rounds win 95.4% | Reconstructed with the stated inputs |
| Aug 30 | R+13.7 | Mike Rounds win 95.4% | Reconstructed with the stated inputs |
| Aug 29 | R+13.6 | Mike Rounds win 95.4% | Reconstructed with the stated inputs |
| Aug 28 | R+13.7 | Mike Rounds win 95.5% | Reconstructed with the stated inputs |
| Aug 27 | R+18.8 | Mike Rounds win 97.8% | Reconstructed with the stated inputs |
| Aug 26 | R+18.9 | Mike Rounds win 97.8% | Reconstructed with the stated inputs |
| Aug 25 | R+21.8 | Mike Rounds win 98.2% | Reconstructed with the stated inputs |
| Aug 24 | R+21.8 | Mike Rounds win 98.2% | Reconstructed with the stated inputs |
| Aug 23 | R+21.8 | Mike Rounds win 98.2% | Reconstructed with the stated inputs |
| Aug 22 | R+21.8 | Mike Rounds win 98.2% | Reconstructed with the stated inputs |
| Aug 21 | R+21.8 | Mike Rounds win 98.2% | Reconstructed with the stated inputs |
| Aug 20 | R+21.8 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 19 | R+21.8 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 18 | R+21.8 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 17 | R+21.8 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 16 | R+21.8 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 15 | R+21.8 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 14 | R+21.9 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 13 | R+21.9 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 12 | R+21.8 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 11 | R+21.9 | Mike Rounds win 98.3% | Reconstructed with the stated inputs |
| Aug 10 | R+21.9 | Mike Rounds win 98.4% | Reconstructed with the stated inputs |
| Aug 9 | R+21.9 | Mike Rounds win 98.4% | Reconstructed with the stated inputs |
| Aug 8 | R+21.9 | Mike Rounds win 98.4% | Reconstructed with the stated inputs |
| Aug 7 | R+21.9 | Mike Rounds win 98.4% | Reconstructed with the stated inputs |
| Aug 6 | R+22.0 | Mike Rounds win 98.4% | Reconstructed with the stated inputs |
| Aug 5 | R+21.5 | Mike Rounds win 97.9% | Reconstructed with the stated inputs |
| Aug 4 | R+21.5 | Mike Rounds win 97.9% | Reconstructed with the stated inputs |
| Aug 3 | R+21.5 | Mike Rounds win 97.9% | Reconstructed with the stated inputs |
| Aug 2 | R+21.5 | Mike Rounds win 97.9% | Reconstructed with the stated inputs |
| Aug 1 | R+21.5 | Mike Rounds win 97.9% | Reconstructed with the stated inputs |
The polls
Poll average R+9.8A poll’s weight halves every 60 days and grows with its sample. Each pollster counts once, at its best release. Every poll counts at its published margin, sponsored or not.In Senate races the forecast then counts a poll sponsored by a party or campaign at a quarter of its weight and moves its margin 2 points against that party, which puts the average it reads at R+11.3. It then applies a fitted correction of 1.6 points toward Republicans for Senate races, measured from past polling error, before blending it with its other evidence.14 recorded polls · 13 in the poll average
| Fieldwork | Added | Pollster | Result | Sample |
|---|---|---|---|---|
| from 2026-10-12 | 3d ago | Mason-Dixon Polling & Research, Inc. ↗ | R+19.0I 37% · R 56% | 500 LV |
| from 2026-10-19 | 6d ago | Emerson College ↗ | R+8.0I 46% · R 54% | 803 LV |
| from 2026-10-17 | 7d ago | Quantus Insights ↗ | R+22.1I 37.3% · R 59.4% | 657 LV |
| from 2026-10-06 | Concord Public Opinion Partners ↗ | I+1.0I 43% · R 42% | 400 LV | |
| from 2026-10-12 | Public Opinion Strategies ↗ | R+17.0I 37% · R 54% | 500 LV | |
| from 2026-08-26 | Lake Research Partners ↗ | I+10.0I 51% · R 41% | 500 LV | |
| from 2026-09-24 | Zenith Research ↗ | R+6.0I 47% · R 53% | 500 LV | |
| from 2026-09-08 | Public Policy Polling ↗ | R+3.0I 42% · R 45% | 629 RV |
How the partisan coordinate was built
Tap an input for its calculation and source.
Displayed values are rounded. This is a modeled partisan coordinate.
Mike Rounds leads Brian Bengs by 15.2 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 presidential margin in 2024 as a share of all votes cast, 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, as a share of all votes cast, from Call the Map's own county sums.
- Same source as Act I's 2024-president reference mark, so the origin lands on it.
Fitted model, above the terrain shown +9.612 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 -19.578 minus starting point -29.190 = 9.612 points.
- For orientation, the presidential results here: 2024 R+29.2, 2020 R+26.2.
- The work: the −19.6 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.
This race’s polls +3.494 points
What this race’s own recent polling adds beyond its prior. The forecast weights each poll for recency and sample size and counts each pollster once; the weights listed here are those of the polls’ own average.
- Emerson College (2026-10-21, n=803): R+8.0 · weight 0.71 in the poll average
- Quantus Insights (2026-10-19, n=657): R+22.1 · weight 0.63 in the poll average
- Public Opinion Strategies (2026-10-16, n=500): R+17.0 · weight 0.53 in the poll average
- Mason-Dixon Polling & Research, Inc. (2026-10-14, n=500): R+19.0 · weight 0.52 in the poll average
- Concord Public Opinion Partners (2026-10-08, n=400): D+1.0 · weight 0.43 in the poll average
- Zenith Research (2026-09-27, n=500): R+6.0 · weight 0.43 in the poll average
- … and 8 more below.
- Poll average R+9.8, from 13 polls · 14 recorded polls. This is the polls’ own average, each poll at its published margin, the figure this page’s poll summary shows. In Senate races the forecast then counts a poll sponsored by a party or campaign at a quarter of its weight and moves its margin 2 points against that party, which puts the average it reads at R+11.3. It then applies a fitted correction of 1.6 points toward Republicans for Senate races, measured from past polling error, before blending it with its other evidence. The forecast gives the polls 98% of the weight against its structural prior for this race, which moves the margin 3.5 points away from Republicans from where it stood before the polls. Eligible polls: latest poll: 2026-10-21 (7 days old).
National environment +3.187 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 2026-10-14: 53% generic-ballot aggregates (D+7.7) · 28% special-election overperformance (D+9.0 across 46 specials) · 20% approval-implied (D+9.1 from net approval -24.3).
- Latest polls — generic ballot 2026-10-14 (14 days old), approval 2026-10-14 (14 days old).
- Generic-ballot average D+7.7 · support factor 0.87 (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 — 12% of the weight is carried that way.
- Blended national environment: D+8.3.
- Applied at full strength to this chamber's races.
- This step’s recorded contribution to the margin is +3.2 D.
- Blended national environment: D+8.3 (updated 2026-10-14).
- Effective poll weight 88%; fundamentals share 12%, carried by the interval (×1.06) 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: +3.2 of this margin.
Structural safeguards −2.260 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 −2.3 D.
These are the fitted model’s named contributions to the partisan coordinate, before the candidate-field calculation.
| Named factor | Contribution |
|---|---|
| FundamentalsThe admitted fitted baseline. Its surviving variables differ by office; the source detail above identifies those used for this race. | −19.58 |
| This race's pollsAdmitted head-to-head polls of this race, recency- and quality-weighted. | +3.49 |
| National environmentThe national environment’s contribution to the prior. Polling can attenuate its influence; this value is not the national polling margin. | +3.19 |
| Structural terrain safeguardA bounded pull toward presidential terrain in heavily partisan states. | −2.26 |
| Other factors | 0.00 |
Where the votes are
The map of this race loads here.
Recent elections
| Election | Result | Votes cast |
|---|---|---|
| 2020 · U.S. Senate ↗ | R+31.5 | 420,219 |
| 2014 · U.S. Senate ↗ | R+20.9 | 279,412 |
| 2008 · U.S. Senate ↗ | D+25.0 | 380,673 |
| 2002 · U.S. Senate ↗ | D+0.2 | 337,501 |
Margins are the Democrat’s share of all votes cast minus the Republican’s.
The money
Mike Rounds ↗
R$3.2Mraised
$2.7M cash on hand
Brian Bengs ↗
I$782Kraised
$51K cash on hand
The tick marks cash on hand. A missing filing stays blank rather than becoming $0.
One more fundraising reportCall the Map · $325
The candidates are comfortably out-fundraising the website covering them. A little rude, perhaps, but statistically unsurprising.
- Received so far
- $325
- Measured compute
- $26,188.58
Ko-fi and Buy Me a Coffee supports are counted as each one arrives. 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.
Supporters are listed by first name and last initial; a username alone is shortened to its first eight characters. Want your full name shown? Say so in your message. Give privately, or leave the name blank, and you are listed as Anonymous, with the platform and date. Supporters who give a name may also be thanked by name in the newsletter.
Thank you to Tom H., ColoradoFlyer, Chris, EW, gbaileym…, True Independent, MT V., JBL, Erin G., Caroline M., Melanie, MKV and 7 more.
Outside spending
Separate from what the campaigns raisedFor and against Brian Bengs$550K
1 spending group
| Group | For | Against |
|---|---|---|
| SOUTH DAKOTA CONSERVATIVE PAC | $0 | $550K |
For and against Mike Rounds$817K
3 spending groups
| Group | For | Against |
|---|---|---|
| DEFEND AMERICAN JOBS | $412K | $0 |
| AMERICAN MISSION | $230K | $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
- Turnout, 2018 midterm
- 52.2% 341,048 ballots
- Turnout, 2022 midterm
- 53.2% 354,670 ballots
- 2024 presidential margin
- R+29.9between the two parties
Turnout is ballots cast statewide as a share of the voting-eligible population. Source: University of Florida Election Lab ↗
Population profile
U.S. Census Bureau, 2022 American Community Survey 5-year estimates ↗
Coverage
2 stories · 2 quotes
- Former Tea Party leader backs Bengs in Senate race; Calls campaign 'front wave' of independent movement ↗
South Dakota Public Broadcasting · Oct 28
- Money is pouring into South Dakota’s U.S. Senate race as people and groups across the country sense a rare chance to support a potentially competitive challenger against a Republican incumbent. buff.ly/bK8Pcie ↗
South Dakota Searchlight · Official · 2d ago
curated state newsroom · recent Bluesky post · named-race match - South Dakota’s independent U.S. Senate candidate, Brian Bengs, said he “would probably not be here in a competitive position today” without the support he’s gotten from a new political party co-founded by a former Democrat and a former Republican. buff.ly/Bc8pARe ↗
South Dakota Searchlight · Official · 2d ago
curated state newsroom · recent Bluesky post · named-race match - Poll: Sen. Rounds leads challenger Bengs 56-37% ↗
South Dakota News Watch · Oct 22
Forecast as of October 28, 2026: Call the Map currently has Mike Rounds ahead of Brian Bengs by 15.2 points, with a 99 in 100 chance to lead. The seat is currently held by a Republican. That result would keep the seat with Republicans. The current poll average is R+9.8; 14 public polls are recorded.