LOS ANGELES (CBSLA) – Five Democratic presidential hopefuls made appearances Friday at a union summit in downtown Los Angeles, preaching their support for organized labor and praising the historical significance of unions.

Former Vice President Joe Biden (L) and Massachusetts Sen. Elizabeth Warren participate in the third Democratic primary debate at Texas Southern University in Houston on Sept. 12, 2019. (Getty Images)

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Former Vice President Joe Biden and Sens. Elizabeth Warren, Kamala Harris and Corey Booker were all on hand – along with former U.S. Secretary of Housing and Urban Development Julian Castro – for the Unions for All Summit which began Thursday and runs through Sunday at the Westin Bonaventure Hotel & Suites at 404 S. Figueroa St.

Biden spoke briefly to reporters in which he condemned President Trump for suggesting both Ukraine and China should investigate dealings between the former VP and his son Hunter.

“This is not about me, this is not about my son, there’s not a shred of evidence of having done anything wrong,” said Biden, who repeatedly referred to the U.S. president as “unhinged.”

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The Ukrainian prosecutor general announced on Friday that his office was reviewing previous cases involving a gas firm with ties to former Vice President Joe Biden’s son, Hunter Biden, CBS News reported.

Sen. Bernie Sanders was also scheduled to appear Friday, but was forced to cancel after undergoing a procedure for a blocked artery.

The appearances by the Democratic presidential hopefuls came on the heels of a new Public Policy Institute of California survey in which Warren, Sanders and Biden were locked in a statistical three-way tie in California.

Saturday will feature Beto O’Rourke, Sen. Amy Klobuchar and Mayor Pete Buttigieg.

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The event, which is not open to the public, is being put on by the Service Employees International Union (SEIU).