**Trader consensus on South Dakota Senate turnout centers on the 350K–400K range because the November 3 general election is a low-salience midterm in a solidly Republican state.** Incumbent Mike Rounds holds a clear lead over independent Brian Bengs in a race rated safe or likely Republican by multiple forecasters, limiting voter mobilization. Historical midterm turnout of roughly 53% of eligible voters, combined with South Dakota’s modest population, points to totals in this band. Rising early and absentee voting—now exceeding 30% in recent cycles—supports the slight edge for the 375K–400K bin, while the approaching October 19 registration deadline and presence of other statewide contests provide modest upward pressure. Limited campaign spending and national midterm patterns keep higher or lower extremes at lower probabilities.