California’s 4th Congressional District holds its top-two primary on June 2, 2026, under the state’s nonpartisan primary system that advances the two highest vote-getters regardless of party. Longtime Democratic incumbent Mike Thompson, a moderate who serves on the House Ways and Means Committee, faces his strongest primary challenge in years from Democrat Eric Jones, a venture capitalist and nonprofit executive who has drawn endorsements and invested substantial personal funds. The redrawn district, which now includes more rural and conservative areas in Yolo and Yuba counties alongside Napa and Sonoma wine country, features multiple Republican candidates split across the field. Thompson’s incumbency advantage and committee role position him as the clear frontrunner to advance, while Jones’s fundraising and visibility create the main contest for the second spot in the November general election.