Incumbent Democrat Mike Thompson leads the June 2, 2026, top-two primary for California's 4th Congressional District after redistricting added rural, traditionally conservative counties including portions of Colusa, Placer, Sacramento, Sutter, and Yuba. Partial results show Thompson at approximately 37 percent, Republican Ray Riehle near 24 percent, and fellow Democrat Eric Jones around 21 percent, positioning Thompson and Riehle to advance to the November general election. The race features a field of multiple Democrats and Republicans, with Thompson seeking his 15th term amid the district's shifted demographics. Official certification and final vote counts remain pending, though major outlets have projected the top-two outcome.