Reports on Wednesday of a surge in advance voting for South Dakota's Republican gubernatorial runoff, attributed by election officials to an influx of party-switchers, prompted a significant repricing in the nomination market. In the session on July 15, 2026, contracts for incumbent Gov. Larry Rhoden to win the GOP nomination jumped 26 percentage points to an implied probability of 89%. The sharp move suggests traders believe the unusual early voting pattern will benefit the incumbent over his challenger, businessman Toby Doeden, in their upcoming July 28 contest.
The market shift represents a decisive consolidation of expectations around Governor Rhoden, who had been trading at 63% prior to the news. In the two-outcome market, probability shifted directly from Doeden, whose contracts fell 25 points to 11%. The high-volume repricing comes after a primary on June 2 where Doeden, a political newcomer, unexpectedly finished first, setting up a competitive runoff with the governor.
Distribution Analysis
| Outcome | Current Prob | Change | Volume |
|---|---|---|---|
| Larry Rhoden | 89% | +26.0pp | 75,592 |
| Toby Doeden | 11% | -25.0pp | 30,586 |
Net: One of two contracts rose on 75,592 in volume, shifting implied probability decisively toward Gov. Larry Rhoden as the likely nominee.
What's Driving the Shift
Surge in Advance Voting and Party Switching: The primary catalyst for the market move was a report from the South Dakota Searchlight on July 15. It detailed that through Monday, 12,617 Republican voters had already cast ballots, a 35% increase over a comparable period before the June 2 primary. County auditors attributed the higher-than-expected turnout to voters changing their affiliation to Republican specifically to participate in the runoff. Minnehaha County Auditor Leah Anderson noted, "We’ve had a lot of people come and change their party, go vote upstairs and then come down and ask to change it right back." This dynamic appears to be interpreted by traders as a motivated effort to support Rhoden or vote against Doeden.
Consolidation of Establishment Support: The June 2 primary was a four-way race, with U.S. Rep. Dusty Johnson and state House Speaker Jon Hansen failing to advance. Doeden finished first with 31% of the vote, while Rhoden secured the second runoff spot with 25%. Traders now appear to be pricing in a scenario where supporters of the more moderate Johnson, who finished a close third with 23%, are turning out in the runoff for the incumbent governor. The influx of new Republican registrants, a total of 7,350 since the primary, is seen as more likely to break for the established governor than for the self-funded outsider candidate.
Market Context
The runoff was triggered because no candidate in the crowded June primary reached the 35% threshold required to win the nomination outright. Doeden, a businessman from Aberdeen, largely self-financed his campaign and branded himself as a political outsider. Rhoden, a rancher from Union Center, ascended to the governorship in January 2025 after his predecessor, Kristi Noem, resigned to join the Trump administration.
The market's near-90% implied probability for Rhoden marks a significant reversal from the primary election results, where Doeden held the momentum. It suggests a strong belief that the structure of a two-man runoff favors the incumbent, who can now consolidate support from across the party.
What to Watch
The key date for this market is the runoff election on July 28, 2026. The contract will settle based on the official nominee declared by the South Dakota Republican Party. The winner will advance to the November 3 general election to face Democrat Dan Ahlers, and will be heavily favored in the staunchly Republican state. Traders will continue to monitor any further reports from the Secretary of State's office on early and absentee voting trends as the election approaches.
