California's 4th Congressional District held its top-two primary on June 2, 2026, in a district rated Solid Democratic. Incumbent Mike Thompson received the most votes at roughly 40 percent, followed by Democratic challenger Eric Jones at about 22 percent. Republican Ray Riehle placed third near 21 percent, with remaining Republican and other candidates trailing further behind. Under the state's nonpartisan primary rules, Thompson and Jones advance to the November 3 general election regardless of party. Trader consensus on the Polymarket reflects these certified primary outcomes, with limited remaining uncertainty tied to final vote certification deadlines in July. The district's partisan composition and redistricting changes after prior cycles shaped candidate fields and turnout patterns leading into election day.