PHILADELPHIA — Bernie Sanders' supporters soundly rejected presumptive Democratic nominee Hillary Clinton on Monday.
The crowd packed into a ballroom at the Philadelphia Convention Center responded with loud boos when Sanders said, "We have got to elect Hillary Clinton.”
Video: Sanders Delegates Boo Clinton at Rally
Sanders addressed his delegates amid heightened divisions in the Democratic Party just a few hours before the opening of the Democratic National Convention.
Democratic National Committee Chairwoman Debbie Wasserman Schultz said Sunday that she was stepping down after the convention amid a controversy over leaked committee emails showing some staffers plotted against the Vermont senator's primary campaign.
When Sanders addressed the Florida congresswoman's resignation, the crowd responded with cheers.
Sanders' supporters disrupted an appearance by Wasserman Schultz at her home state delegation's breakfast Monday. And his supporters predicted further disruption on the convention floor if the chairwoman addressed the convention.
The Bernie Delegates Network, which claims more than 1,200 delegates in its ranks, said its members were discussing possible protest actions during the convention.
Norman Solomon, the head of the delegate network, said he had not heard from the Sanders campaign about not protesting. But Karen Bernal, who heads the California delegation, said she had heard indirectly that Sanders campaign staffers were concerned about disruptions.
Sanders did not tell his supporters to avoid protesting or demonstrating at the convention. He instead attempted to say, over the crowd's displeasure, that Donald Trump would be a disaster as president, and that he did not respect the Constitution.
The delegate leaders rejected notions that they could hurt the Democratic Party's chances of unity heading into the general election, by acting on their disapproval of Clinton, and therefore helping Trump win the presidency.
"We don't want to see Donald Trump taking the White House," said Bernal. "We need to be able to show that there is a space for this kind of discontent within the party and understanding, that we can still move forward and try to do everything that we can to make this a more progressive party."
Sanders spent much of the rally laying out his campaign's victories, including more than 20 primary and caucus victories and nearly 1,900 pledged delegates.
He also encouraged supporters to keep his political revolution going, and support candidates up and down the ballot in November who promote progressive policies.
Campaign organizers passed out papers to attendees encouraging them to sign up and host kickoff events for "Our Revolution ," a new political organization to recruit progressive candidates. Sanders said he would support 100 of them across the country.
"We continue to fight," he said.