Lt. Gov. Gavin Newsom, former Los Angeles Mayor Antonio Villaraigosa, state Treasurer John Chiang, and former state Superintendent of Public Instruction Delaine Eastin made the pitch for support from the National Union of Healthcare Workers.
The two candidates seeking the Republican nod, John Cox and Travis Allen, did not attend, but the union says they were invited.
Questions at the forum focused on healthcare, but also delved into a wide range of other issues, including worker and immigrant rights and how the state should respond to the Trump presidency.
The election is scheduled for Nov. 6, 2018.