PHILADELPHIA (AP) — Bernie Sanders on Monday readied a simple message to his backers at the Democratic National Convention: Unite behind Hillary Clinton to defeat Donald Trump in November.

But many of Sanders’ die-hard delegates, frustrated with the primary process and furious with the outgoing party chair, were still weighing ways to disrupt the four-day event.

Sanders was set to meet privately with supporters before the start of the convention, hours after his loyalists heckled party chairwoman Debbie Wasserman Schultz at a Florida breakfast in her first appearance since her decision to step down.

The Vermont senator was headlining the convention’s first night amid lingering angst over the primary process and plans by some of his supporters to boo Wasserman Schultz when she gavels in the convention. There appeared to be no consensus among the Sanders delegates of how they would influence the convention and some suggested they may turn their backs on Virginia Sen. Tim Kaine, who was recently chosen as Clinton’s running mate.

Also unclear was whether Sanders would release his delegates and back Clinton by acclamation or whether the Sanders’ loyalists would demand a roll call on Kaine’s nomination amid concerns that he is too centrist.

“Hillary has not earned my vote. She has to prove that she has walked the talk,” said Eric Reynolds, a Sanders delegate from Contra Costa County in California. He said he planned to boo Wasserman Schultz.

Norman Solomon, coordinator of an independent network of Sanders delegates, said that Wasserman Schultz’s resignation doesn’t represent “her being tossed overboard by Hillary Clinton,” noting that she’ll have a role with the campaign.

He also questioned the timing of her departure at the end of the convention, during which she will still play a role.

“She’s resigning as of Friday? Why wait until Friday?” Solomon said.

Solomon, whose group communicates with 1,250 Sanders delegates, said supporters were weighing a number of floor protest actions this week. He said the Sanders campaign had not contacted his group to encourage them to not protest.

Sanders, for his part, has struck a positive message in recent interviews, expressing his support for Clinton and the need to project unity. His campaign helped approve a number of provisions in the party’s platform, from a $15 an hour federal minimum wage to an expansion of health care.

“I’m proud that, in the Democratic platform that was passed a few weeks ago, we are making some real progress,” Sanders said on CNN Sunday. He added: “My focus right now is defeating (Donald) Trump, electing Clinton, electing progressive candidates around this country and focusing on the issues that matter the most to working families.”

Efforts to promote party togetherness were not helped by the publication last week of thousands of hacked emails, some of which suggested the DNC was favoring Clinton during the primary season. For many Sanders fans, the messages proved that their concerns about party officials preferring Clinton were correct.