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SAN DIEGO — In a surprising show of discontent with one of California’s most enduring political leaders, the state Democratic Party declined to make an endorsement in this year’s U.S. Senate race on Sunday, snubbing Sen. Dianne Feinstein in her bid for a fifth full term.

Her main challenger, State Senate leader Kevin de León, won the support of 54 percent of delegates at the state party convention here this weekend, short of the 60 percent needed to secure the party’s endorsement. Feinstein received only 37 percent of the votes.

The rebuke of Feinstein by the party delegates comes even though the 25-year incumbent has led polls by wide margins and received the backing of political luminaries like Sen. Kamala Harris and House Minority Leader Nancy Pelosi.

The results were a sign of unrest among many liberals who believe Feinstein should do more to challenge President Trump — and a testament to de León’s insurgent message resonating with the party’s activist left flank. “The outcome of today’s endorsement vote is an astounding rejection of politics as usual,” he said in a statement.

Most California voters say they don’t know enough about de León to have an opinion about him. But he had a much more active presence than Feinstein at the convention, working the crowds and hustling between caucus meetings in white sneakers on Friday night.

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Feinstein’s campaign still has a huge financial upper hand over de León, as well as the built-in advantages of incumbency. Her chief political strategist Bill Carrick played down the importance of the non-endorsement Sunday, arguing it would have little tangible benefit for de León. “The reality is, he’s way the hell behind,” Carrick said.

The party also made no endorsement in the governor’s race, the other big statewide contest this year, which has a more crowded field of Democrats. Lt. Gov. Gavin Newsom led with 39 percent of the delegates, compared to 30 percent for State Treasurer John Chiang, 20 percent for former state schools chief Delaine Eastin, and just 9 percent for former Los Angeles Mayor Antonio Villaraigosa.

In a blow to party leaders’ efforts to consolidate support in key congressional districts, no candidates secured enough votes to lock down the party endorsement in two open seats represented by retiring Republican Reps. Darrell Issa and Ed Royce.

And delegates didn’t settle on a candidate in the races for lieutenant governor and state attorney general either.

Losing the party endorsement doesn’t always mean much. When Feinstein ran for governor in 1990, she dramatically declared her support for capital punishment at the state convention, over loud boos from the hall. The party’s delegates endorsed her more liberal rival, Attorney General John Van de Kamp. But Democratic voters as a whole agreed with Feinstein on the issue, and she won the primary that year.

Feinstein also lost the party endorsement during her first run for Senate in 1992.

“The people who are motivated to give up a weekend to show up at a party convention are further off the middle of the political spectrum,” said Darry Sragow, a political analyst and Feinstein’s 1990 campaign manager, who is not involved with this year’s Senate race.

Still, the results showed the party faithful’s movement to the left. Both campaigns fought hard to court delegates’ support, and the contest was a “test of the establishment’s authority and power,” de León chief of staff Dan Reeves said before the vote.

The endorsements were announced around 1:45 a.m. on Sunday after a prolonged vote-counting process, with delegates getting kicked out of the San Diego Convention Center as they waited for the results.

In his speech to the convention hall on Saturday afternoon, de León drew a series of contrasts with Feinstein without mentioning her name, saying he would have voted against the Iraq War and domestic wiretapping and he would never be “fooled into believing Donald Trump can be a good president” — a reference to a Feinstein comment that raised the ire of the left last year. He also highlighted his upbringing as the son of an immigrant housekeeper a few miles away from the convention center.

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Feinstein focused her address on gun control, calling an assault weapons ban “my mission” and “my quest” in the aftermath of the deadly school shooting in Parkland, Fla. this month. But she ran out of time for her speech, and was played off the stage by music. “I guess my time is up,” Feinstein said, and de León supporters shouted back, “time’s up!”

A third candidate, lawyer Pat Harris, got the support of 5 percent of delegates, while 3 percent voted for no endorsement.

Research suggests that the party endorsement is a bigger deal in lower-profile races than in statewide contests like the Senate race, where voters have more information about the candidates. Thad Kousser, a political science professor at UC San Diego, studied the effect of the party endorsement in 2012 and found that it gave candidates in downballot campaigns about a 10 percent boost.

In several other of the state’s competitive Republican-held congressional races, candidates Hans Keirstead, Dave Min and Jessica Morse won the Democratic endorsements in their respective districts. Several of Min’s opponents tried to convince delegates to undo his endorsement Sunday, arguing that he wasn’t progressive enough, but they were unable to secure enough support to do so.

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Hundreds of Catholics gather in San Francisco to decry COVID-19 limits on worship The party also voted to oppose an endorsement for State Sen. Tony Mendoza, who resigned this week amid sexual misconduct allegations and attempts to expel him but is running for re-election. No endorsement was made in his Los Angeles-area district.

Mendoza declined to speak at the nominating caucus, but he told reporters he was not deterred. “It’s like every other election,” he said, “you talk to the voters and you let them know what your message is about and what you’ve done.”

An investigation by independent lawyers hired by the Senate found that it was “more likely than not” that Mendoza, who is married, had subjected six women to unwanted sexual advances.

The party did endorse Assemblywoman Cristina Garcia, who is on leave during a separate investigation into sexual harassment allegations against her, including that she groped a male staffer. The endorsement was made at a local caucus before the allegations went public, and unlike in Mendoza’s case, Democratic Party regulations gave delegates no option to undo it.

Party chair Eric Bauman referred to Garcia’s endorsement as an “elephant in the room,” telling delegates he had met with lawyers and concluded there was no way to reverse it. “That’s the kind of thing that our rules have not contemplated,” he said.