In the June primary, de León got only 12 percent of the vote — compared to Feinstein's 44 percent — and narrowly made it to the November election under the state's top-two primary system.

“I mean, this was not a close primary election, and there were 32 people on the ballot,” Feinstein said at a "party unity" breakfast on Saturday morning. “I take nothing for granted. We work hard. I work hard.”

She said then that even if de León did get the endorsement, it would not change her campaign.

Feinstein’s supporters spent the day arguing that the Democrats need her seniority and experience in the Senate to most effectively push back against the agenda of President Trump and congressional Republicans.

"I think there are a lot of 'Berniecrats' who would like to support de León and they think about change,” said board member Julie Soo early in the day. “Change is good but not in tumultuous times like we are now, and we need some continuity. ... In Washington, D.C., you don’t get the good committee spot when you’re a newbie.”

But supporters of de León are promoting a different strategy to fight back against Republican policies. They say Feinstein has lost her edge, and de León would breathe new life into the Democratic Party.

“I’ve known Dianne Feinstein since she was mayor of San Francisco, and she’s done a good job and I’ve got no problem with her at all,” said board member Domenic Torchia before the vote. “It’s just time that we get some young blood in there and start moving on to get rid of the Trump administration [and] all the damage they’ve done.”

The meeting continues on Sunday with votes expected on the 12 statewide measures appearing on the November ballot, including Proposition 10, which would repeal the Costa-Hawkins Rental Housing Act.