Oregon’s all-mail voting system has historically produced strong general election participation, with the 2022 midterm reaching 62.3% turnout and the May 2026 primary setting a record 1.28 million ballots cast at 41.9%. Traders see the November 3 U.S. Senate contest between incumbent Democrat Jeff Merkley and Republican David Brock Smith as likely to fall in the 1.8–2.2 million range because a safe Democratic seat offers limited mobilization incentives while the established mail infrastructure and October ballot distribution support baseline participation near recent midterm levels. Recent Supreme Court action on federal mail-voting directives has introduced procedural uncertainty, yet state officials have directed counties to maintain current procedures, preserving the factors that keep probabilities clustered across several adjacent bins. Clear separation could emerge from final registration figures, any late legal shifts affecting ballot access or curing, or unusually high or low engagement driven by concurrent statewide races.