BURLINGTON, Vt. — By now, Sen. Bernie Sanders, I-Vt., has gotten used to supporters urging him to run for president in 2020; at rallies, at airports, on his weekday walks to the Capitol. At a recent gathering here, Greek economist Yanis Varoufakis went further: Only Bernie Sanders could save the world.

“Let me convey a message from all of us in Europe, for all those comrades of yours who are now struggling to reclaim our cities, our world, our world, our environment,” Varoufakis said. “We need Bernie Sanders to run for president.”

The senator from Vermont, who is actively discussing whether to mount another campaign, smiled and closed the session. But over three days at the Sanders Institute’s inaugural conference, the senator and his supporters described a democracy under attack by populist right-wing forces as compromise-hungry “neoliberals” lacked a vision to defend it — a dynamic they see as leading to President Donald Trump’s win in 2016.

Even as Democrats won back the House of Representatives last month, some high-profile left-wing candidates fell short, a dynamic Sanders struggled with; he opened the weekend conference by saying the party could have done better. For the senator and his supporters, it was clear that Democrats had squandered power when they last held it, leading to a surge of right-wing nationalism. To avoid a repeat, the left needed to organize — preferably, many here believe, with Sanders in the White House.

“Neoliberal establishments are collapsing, not just here, but around the world,” said Cornel West, a crusading academic who endorsed Sanders in 2016 and backed the Green Party’s campaign when Sanders lost the primary. “The only thing presented (to people) that has some credibility is vicious, authoritarianism fascism. If we don’t have a left populism that’s credible, we’re running down a fascist road.”

West, who has encouraged Sanders to run as a third-party candidate, said in an interview that the senator looked to be committed to his work inside the Democratic Party. And even at the conference, an invitation-only affair for around 250 people, there was speculation that another candidate could pick up Sanders’s banner in 2020.

Author Naomi Klein told a Friday audience that support for a “Green New Deal,” a jobs plan based on a transition away from fossil fuels, would be essential for “any candidate who wanted to run as a progressive in 2020,” Sanders or otherwise. Rep. Tulsi Gabbard, D-Hawaii, who spoke at the conference Saturday, is actively exploring her own presidential bid. No Democrat seen as a potential nominee, said West, came with as much “baggage,” where the left was concerned, as Hillary Clinton had.

Sanders, 77, has frequently praised the ways Democrats adopted his “really radical ideas” — he uses the term sarcastically — during and after the 2016 election. It started with the drafting of a more left-wing platform and continued this year as a record number of House and Senate Democrats and Democratic candidates endorsed the main planks of the Sanders movement — Medicare-for-all, free college tuition and a $15 minimum wage.

Several candidates who had lost races this year also made it to Burlington, saying they would come away thinking that the movement had been dealt a temporary defeat and was still reshaping the Democratic Party, while potentially allowing other candidates to compete in the same 2020 lane as Sanders.

“Some (potential presidential) candidates have reached out to me since the midterms,” said Randy Bryce, a union organizer who lost an expensive and closely watched House race in Wisconsin, running on a Sanders-style platform of universal Medicare and abolishing Immigration and Customs Enforcement. “They’re interested in the message. Once people are educated on what Medicare-for-all involves, it can be popular throughout the country.”

But for many at the conference, the only clear way to pull that off was to nominate Sanders, who ended the 2016 primaries with nearly 14 million votes and with high favorable ratings. In October, a Gallup poll put Sanders’s favorable rating at 53 percent; it has been above 50 percent ever since his primary bid gained steam three years ago. Polls that test Sanders against Trump consistently show Sanders with a lead, though at this point in the 2016 cycle, polling showed Trump badly trailing in a matchup with Clinton.

“Since we need to take such bold steps forward, it might be that we need someone who’s been clear and consistent for 40 years,” said John Cusack, an actor and activist. “I hope to God that he runs and wins. What makes me hopeful is that when I talk to millennials and younger people, they get it. They love Bernie. They want a future.”

The risk, said Sanders’ supporters, was bigger than one more lost election. A major theme of the weekend was that the international left had failed to organize as effectively as the nationalist right. Varoufakis’ remarks Friday ended with the launch of Progressive International, an effort to build ties and share strategies between left-wing activists and parties across the world. Sanders campaign veterans, separately, had already been training left-wing parties in Europe on the tactics used in the 2016 campaign.

“After the (2008 economic) crisis, two kinds of people united internationally: bankers and fascists,” Varoufakis said.

Sanders himself has argued that the “post-World War II global order,” which in many countries responded to the Great Recession of 2007 to 2009 by cutting back social services. This, he says, enabled the rise of candidates who appealed to fear of changes both economic and demographic, like Trump, Brazil’s Jair Bolsonaro, and of right-wing governments in countries like Italy and Hungary.

Fernando Haddad, the left-wing politician who lost to Bolsonaro after courts barred popular former president Luiz Inácio Lula da Silva from running, said in an interview that his country was “harvesting the consequences of the neoliberal project’s failure.” At weekend panels, Sanders supporters argued that Democrats had created the opening for Trump by failing to crack down on industries, like health insurance and banking, that many voters saw as exploitative.

For Sanders die-hards, there was no longer any question that he would be the best possible candidate to reverse the gains of right-wing nationalists. RoseAnn DeMoro, who had turned National Nurses United into the biggest labor backer of Sanders’s 2016 bid, took every chance she could to urge the senator to run again. Asked if she had been contacted by other presidential hopefuls, DeMoro was incredulous.

“There are no other candidates,” she said.