Sen. Dianne Feinstein (D-CA) will get a left-wing challenge from a rising Democratic star.

According to CNN, California Senate President Kevin de Leon (D) will run for the Senate, pitting him against the longtime senator in an all-party primary.

De Leon has been mulling a run for a while, and has received a lot of encouragement from progressives who are fed up with Feinstein’s relatively moderate positions — and how blandly she’s talked about much of President Trump’s actions.

His run could set up the first serious left-wing challenge of a sitting Democrat in recent memory. Feinstein, 84, recently announced she’d run for reelection. But California’s unique all-party primary system could make her hard to defeat. The top two vote-getters in a primary advance to the general election, and if two Democrats advance — a real possibility — Feinstein could draw Republican votes.

The race will likely be defined generationally — de Leon is 50 — as well as geographically and racially, as the Latino de Leon is Los Angeles-based in a state where northern Californians like Feinstein have long dominated politics.

He’s not the only one looking at a bid: Billionaire environmentalist Tom Steyer is also rumored to be mulling a run, though Steyer did so two years ago before deciding not to challenge now-Sen. Kamala Harris (D-CA).