“I have known Sen. de León for years and have fought alongside him on immigrant rights, expanding health care, and climate change,” Tom Steyer (right) said in a prepared statement. | Charley Gallay/Getty Images for Global Green Billionaire Steyer endorses de León over Feinstein

LOS ANGELES — Tom Steyer, the billionaire Democratic mega-donor, is endorsing Kevin de León in his longshot bid to unseat California Sen. Dianne Feinstein, the latest rebuke of Feinstein from her party’s increasingly agitated left flank.

Steyer’s endorsement – if followed by outside spending – could improve de León’s standing in a race that he has so far failed to make competitive. Feinstein, a centrist Democrat, holds a massive advantage over the progressive state senator in both fundraising and public opinion polls.


“I have known Sen. de León for years and have fought alongside him on immigrant rights, expanding health care, and climate change,” Steyer said in a prepared statement. “Our work together on behalf of all Californians has assured me that he would be a champion of California's priorities and values. Kevin de León has proven himself to be the best of the next generation, and I am proud to support him for U.S. Senate.”

The endorsement was not unexpected. Steyer once considered challenging Feinstein himself, and he has appeared on cable television previously as a near-surrogate for de León. Earlier this year, Steyer described the contest on MSNBC as “incrementalism versus visionary thinking in the Democratic Party.”

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Lauded by many young, progressive activists in California, de León in February deprived Feinstein of her own state Democratic Party’s endorsement, outpolling her by 17 percentage points in the delegate vote.

But the state senator remains largely unknown to the broader electorate in California. Feinstein leads him 42 percent to 16 percent among likely voters, according to a Public Policy Institute of California poll last month.

The race between Feinstein and de León is unlikely to be decided before November. With no prominent Republican running in the state’s top-two primary in June, Feinstein and de León are both expected to advance to the general election.

