South Carolina's 2026 U.S. Senate contest features an open Republican seat after the July death of four-term incumbent Lindsey Graham, with Darline Graham and Ralph Norman advancing to an August 25 runoff while Democrat Annie Andrews secured her party's nomination. This special context, combined with midterm-year dynamics in a solidly Republican state, has produced closely matched trader probabilities across multiple turnout bins from under 1.4 million to over 2.2 million votes. Historical midterm participation rates near 43 percent of eligible voters provide a baseline, yet the race's condensed timeline, ongoing primary enthusiasm questions, and variable factors such as early voting mobilization and national political conditions sustain the even distribution of implied probabilities. Scheduled runoff results and subsequent campaign intensity through November could shift expectations by clarifying voter engagement levels.