California's 4th Congressional District held its June 2, 2026, top-two primary under the state's nonpartisan system, with incumbent Democrat Mike Thompson seeking reelection in a district reshaped by prior redistricting that incorporated additional rural counties. Early and partial returns show Thompson leading at roughly 39%, followed by Republican Ray Riehle near 22% and Democrat Eric Jones near 21%, with remaining Republican candidates splitting the rest of the vote. Trader consensus on the primary winners market reflects Thompson's strong incumbency position and expected advancement alongside one other candidate, while Jones trails closely enough that outstanding ballots could shift the second slot. The general election matchup will be set once full results are certified.