Three Democrats, four Republicans, and one independent candidate are running in the top-two primary for California's 4th Congressional District on June 2, 2026. As of March 2026, incumbent Mike Thompson (D) and Eric Jones (D) led in fundraising and local media attention.

Local political observers describe the primary in terms of the ideological and generational contrast between Thompson and Jones. The San Francisco Chronicle's Joe Garofali described the primary as "another example of a younger, well-funded Bay Area Democrat taking on an entrenched candidate as the Democratic Party grapples with how to win back voters," referring to the party's losses at the national level in the 2024 elections. Politico's Jeremy B. White said Jones is "hoping to exploit a rapidly shifting media landscape that makes it easier for lesser-known candidates to break through, as Zohran Mamdani did in New York’s mayoral primary with viral campaign videos." The Press Democrat's Phil Barber said, "Democrats hold an overwhelming edge in voter registration in the district, so the June primary is set to decide the likely frontrunner in the November election."

Thompson was first elected to the House in 1998. He earlier served eight years in the California Senate. Thompson is a vineyard owner. Thompson says he is running because "[w]ith the outcome of the last election and what’s happened since then with this (Donald Trump) administration and the Republican majority, it’s absolutely imperative that I continue the work I’ve started," referring to his position on the House Ways and Means Committee. The Democratic Party of California endorsed Thompson.

Jones is a former executive at an investment firm and the founder of the American Dream Institute, a group describing itself as "a first-of-its-kind digital engagement engine dedicated to helping the Democratic Party rebuild trust with young working Americans." Jones says he is running "to restore the American Dream for every family — not just the wealthy few."[7] Our Revolution, an organization that advocates for the policies of Sen. Bernie Sanders (I-Vt.), endorsed Jones.

Also running in the primary are Trevor Merrell (D), Sharon Brown (R), Heath Fulkerson (R), Mandy Ghusar (R), Laurie MacKenzie (R), and John Wesley Tyler (I).

In a top-two primary, all candidates running for a given office appear on the same ballot. The top two finishers—regardless of partisan affiliation—advance to the general election. One Democrat and one Republican have advanced from every top-two primary in the 4th District since 2016.

The primary is taking place in the context of redistricting in California that changed the 4th District's boundaries from those used in 2024. Inside Elections' Nathaniel Rakich said the 2026 version of the 4th District favors Democrats overall but does so by a narrower margin than the district lines in use in 2024. As of March 2026, major election forecasters rated the general election Solid/Safe Democratic.