South Dakota's at-large House race features Republican Marty Jackley against Democrat Nikki Gronli in an open seat previously held by retiring GOP incumbent Dusty Johnson. Jackley's primary win and consistent polling leads of roughly 20 points or more align with the district's deep Republican lean, reflected in trader pricing that places the most likely victory margin in the 20-25 point range. The absence of major late-campaign shifts, such as significant endorsements, scandals, or turnout surprises in the final weeks, has kept probabilities stable around these levels. Early voting data and the state's partisan baseline continue to anchor expectations for a comfortable Republican outcome on November 3, with limited scope for Democratic gains absent unusual developments.