In the low-salience 2026 South Dakota U.S. Senate contest, incumbent Republican Mike Rounds faces independent challenger Brian Bengs after the Democratic nominee withdrew in August, limiting voter mobilization and keeping the race noncompetitive. Historical midterm turnout in the state has ranged from roughly 350,000 to 355,000 ballots in 2022, well below presidential-year levels near 430,000, while the July primary drew just 118,000 votes amid typical off-year dynamics. With few high-profile issues or campaign events to drive engagement, registered-voter participation is expected to settle in a narrow band around recent midterm baselines. The closely matched market prices across multiple turnout buckets reflect this uncertainty over baseline participation rates and any late-cycle factors such as weather or targeted get-out-the-vote efforts that could modestly shift totals.