Khadijah Shareef, right, and Denise Valkyrie, both of Indiana, speak between sessions during the People's Summit in Chicago on June 10. The three-day event features speakers from the left-wing political movement, including Bernie Sanders. ( Alyssa Schukar for The Washington Post )

The groans began as soon as Hillary Clinton came on-screen.

It was the first day of the People’s Summit, a progressive conference organized by groups connected to Sen. Bernie Sanders (I-Vt.), and an organizer was showing hundreds of activists a video demonstrating right and wrong ways to “build a movement that will win.”

The wrong way: Clinton’s caught-on-video response at a 2016 fundraiser to a Black Lives Matter protester demanding she apologize for having used the term “super predators” a decade earlier, during her husband’s push for tougher sentences for violent criminals. Groans turned to jeers as the video showed the protester being removed.

The right way: Sanders’s tactic in an August 2015 appearance of standing back and letting activists who interrupted him at a Seattle rally take over the event. Cheers filled the McCormick Place meeting room, where the People’s Summit had convened, as Sanders was shown on the screen talking to BLM organizers.

“That’s one way to link different issues up to one movement,” said Erin Evans, an organizer at one of Sanders’s biggest backers, National Nurses United, who was giving the presentation. “There is a way to bond people through a common vision while at the same time acknowledging that forms of structural violence that some communities undergo are important.”

Sanders was introduced by NNU Executive Director RoseAnn DeMoro as a politician who had “been rejected by those who control the party and their moneyed interests.” Onstage, he congratulated the Labour Party for its gains in the U.K.’s elections, and recounted the wins of his campaign — 2.5 million individual donations, 46 percent of the primary vote, landslides with young voters.

“We may not have won the campaign in 2016, but there is no question that we have won the battle of ideas,” Sanders said. “Brothers and sisters, that is no small thing.”

Nearly a year after effectively conceding the Democratic presidential nomination, Sanders was the star of this year’s People’s Summit, which has quickly become the country’s largest progressive political conference. At least 4,000 people trekked to Chicago for a weekend of teach-ins, panels and dance parties. In a Saturday-night speech, Sanders planned to tell activists to charge ahead because “ideas that, just a few years ago, seemed radical and unattainable, are now part of Main Street discussion.”

But as Sanders used his star power to unite activists behind the Democrats, some debated whether the Democratic Party could ever be fixed to their liking. Faced with unified Republican control of Washington, progressives were less interested in simple unity than in a purity that they believed could win.

Much of the discussion at the People’s Summit focused on the need to leave “neoliberal” politics in the dust. But there was disagreement about how to do so.

On Friday night, activists cheered at a clip of the NNU’s DeMoro telling California Democrats not to “assume the activists in California and around this country are going to stay with the Democratic Party.”

When Clinton’s campaign was mentioned at all, it was as a cautionary tale.

“A billion dollars, and they set it on fire!” said CNN commentator Van Jones in a passionate speech. “A billion dollars for consultants!”

There were also comparisons to the surprise surge of the Labour Party in Thursday’s British election. Like Sanders, Labour leader Jeremy Corbyn did not win. But Prime Minister Theresa May lost her majority, and Labour made gains that defied conventional wisdom.

“It didn’t seem like [Corbyn] was talking about how bad Theresa May was, or how stupid those Brexit voters were,” said Larry Stafford Jr., executive director of Progressive Maryland, at a panel on post-Sanders campaign organizing. “It seemed like there was a progressive Labour platform. They talked about their ideas; Democrats focus too much on personality.”

Candidates for Congress and local offices walked the halls of the convention, signing up activists, who — post-Sanders — felt that any race was winnable if a candidate ran to the left.

“Before the 2016 election, people would show up to the ballot box and cast a vote,” said Winnie Wong, a co-founder of People for Bernie, a group that grew out of the Occupy movement. “They wouldn’t feel empowered. The agenda was always set by the media and the parties.”

More hotly debated was what role Sanders himself would play in crafting the agenda — and whether the Democratic Party was worth saving at all, a topic that played out in common areas and after-parties.

Stephen Jaffe, a 71-year-old Sanders supporter challenging House Democratic leader Nancy Pelosi for the 2018 midterm elections, spent some of a Friday-night meet-and-greet debating the relevance of the party with would-be supporters.

“If the driver pulls the car into a ditch, you get a new driver,” said Jaffe.

“What if the car’s so banged up that no one wants it?” asked an organizer for a group that aimed to draft Sanders as an independent 2020 presidential candidate.

In an interview with The Washington Post, Sanders reiterated that he had become the Democrats’ outreach chair in the Senate; third-party politics in the wrong places would only split the movement, he said.

“Look, as the longest-serving independent member of Congress, I know something about that,” Sanders said. “Where my energy is right now is in fundamentally transforming the Democratic Party into a grass-roots progressive party.” And we’ll see where it goes.”

But the long hangover from the 2016 campaign has lingered. Melissa Byrne, a Sanders organizer who now serves on the Democratic National Committee’s transition committee, said she continues to spend time and energy persuading people not to abandon the party over bitterness about the DNC’s perceived slant toward Clinton.

“For the most part, people are past the primary [season],” she said. “There’s not one person to coalesce around, so there’s a lot of fighting against something, not fighting for one thing. And when you’re fighting against something, like Occupy did, it gets messy.”

Rep. Ro Khanna (D-Calif.), a freshman who has become the face of the Justice Democrats political action group, which was set up to beat “corporate” incumbents in primaries, said there was such a thing as too much negativity.

“There’s a populism that goes after a villain, and there’s a populism that’s aspirational,” Khanna said. “Aspirational populism cuts across the party. It means talking about single-payer health care. It means the bill I’m working on with [Sen.] Sherrod Brown [D-Ohio] to expand the Earned Income Tax Credit. Six months ago, people said that was crazy. And now everyone who might run in 2020 is calling and asking if they can endorse it.”

In Republican-controlled Washington, and in most states, the ideas are stalled. Sanders, who will turn 79 before the next election, was beseeching people not to wait on him to save them. In Chicago, they obliged.

Naomi Klein, an author promoting a book on how the anti-Trump resistance needs to advance, said at a Saturday panel that the collapse of “neoliberalism” and the unpopularity of the Trump administration has driven the political conversation.

“We’re seeing that we were lied to — we’re seeing that radical ideas are popular,” Klein said. “What’s next? Reparations for slavery and colonialism? Worker co-ops at the centerpiece of a democratic economy? Who knows?”