Incumbent U.S. Senator Mike Rounds holds a commanding position in the South Dakota Republican Senate primary due to his established record, substantial fundraising edge exceeding several million dollars compared to challenger Justin McNeal’s minimal resources, and an endorsement from President Trump. McNeal, a Navy veteran and businessman, filed as the only other Republican candidate ahead of the June 2 primary date, but polling from earlier this spring showed Rounds leading by a wide margin. Kristi Noem, who resigned as governor last year, is not a candidate. The Republican nomination in this deeply Republican state effectively determines the general election outcome. A challenge to the current trader consensus would require an unforeseen late surge by McNeal or extremely low turnout favoring the underdog, neither of which recent developments indicate.