The Forecasting MachineOpen interactive report

Will Brian Bengs (I) win the South Dakota U.S. Senate election on November 3, 2026?

Resolves Yes if Brian Bengs (I) is certified as the winner of the South Dakota U.S. Senate seat contested on November 3, 2026, and No otherwise. If the contest is not decided on election night — because of a runoff, a ranked-choice tabulation, or a recount — it resolves on the final certified result. Declared candidates: Brian Bengs (I); Mike Rounds (R).

Forecasted on

Forecast probabilities

  • Yes: 3.6%
  • No: 96.4%

Reasoning

Bengs has a plausible but narrow path: the closest independent poll shows him trailing by eight points, and the national mood appears favorable to Democrats. The broader evidence—South Dakota’s Republican lean, Rounds’s strong approval, and most late polling—still points firmly the other way: Yes 3.6%; No 96.4%.

Yes — A real opening, but a long shot

Bengs is the sole major opposition candidate after Democrat Julian Beaudion withdrew, removing the risk that anti-Rounds votes split across two challengers [e56, e93]. The KELOLAND/Emerson poll put Rounds ahead 50% to 42%, a closer contest than several other surveys suggest, and Mason-Dixon found Bengs leading among independent voters 62% to 30% [e50, e54, e59]. A Lake Research Partners poll even showed Bengs ahead, though that result stands apart from most of the late polling [e76].

There are signs of a broader independent coalition: the Forward Party and Independent Center endorsed Bengs, while Andrew Yang, Christine Todd Whitman, and Adam Brandon appeared with him at campaign events [e128, e129, e133, e126]. Bengs has also emphasized ethics and independence. Meanwhile, national polls show Democrats with a substantial generic-ballot lead, and early-voting data point to stronger Democratic participation nationally [e138, e141, e149, e145]. Those trends could give Bengs some lift, but they do not show that voters in South Dakota are moving toward him at the scale he would need.

No — The fundamentals and polling favor Rounds

South Dakota’s federal-election baseline is strongly Republican [e21, e32]. Rounds has the additional advantages of incumbency and a 61% job-approval rating in the South Dakota Poll [e124]. His campaign also has far more cash on hand—about $1.75 million to Bengs’s $146,000 in the latest reported figures—and Republican candidates held a statewide get-out-the-vote bus tour [e11, e125, e127]. The U.S. Chamber of Commerce also endorsed Rounds [e75].

The polling is not unanimous, but its weight favors the incumbent. Besides the closer Emerson/KELOLAND result, the South Dakota Poll found Rounds ahead 56% to 37%, and Quantus reported a 57% to 36% lead; other surveys also put Rounds well ahead [e53, e57, e58, e103]. Bengs’s favorable polling includes a survey commissioned by his campaign, while the independent surveys mostly show a substantial Rounds advantage [a1, e76]. Rounds’s strong showing in his Republican primary and his large wins in prior elections reinforce the structural case for him [a5, a10].

Why the probabilities are so lopsided

The closer poll and national Democratic advantage keep a Bengs upset from being impossible. But he would need a major polling error or late movement in his favor, in a state where the incumbent is popular and most available surveys show him leading—often by a wide margin. The evidence therefore supports a 3.6% chance of Yes and a 96.4% chance of No.

Update summary

There is no material change in the evidence: campaign endorsements and appearances, the Republican bus tour, and national polling and turnout trends were already part of the prior assessment [e128, e129, e133, e125, e138, e145]. With no consequential new development and Election Day closer, the outlook changes only marginally.

Cited evidence