“The progressive left is ascendant in this country!” bellowed Representative Keith Ellison of Minnesota, delivering the closing keynote of Netroots Nation in St. Louis earlier this month to mostly fellow Bernie Sanders backers. “Your activism is driving this moment and will drive the next year.”

For most of the 2016 primaries, that’s how it’s looked: Sanders’s improbably effective insurgent campaign not only brought in millions of young progressives, it pushed Hillary Clinton further and further left on a succession of key issues. Ellison and his cadres have reason to celebrate their newfound influence over the party. But a one-two punch on the eve of the Democratic National Convention in Philadelphia has many wondering anew: Is the left really driving the moment, or about to get run over again?   

It was bad enough, for many on the left, when Hillary Clinton tapped centrist Virginia Senator Tim Kaine for vice president, rekindling anxieties about the nominee running back to the center. Kaine’s positions on trade, fossil fuels, and labor rights (to name a few) have not, let’s say, endeared him to the left, which sees him as a “Wall Street Democrat” through and through. But Friday’s revelation of a WikiLeaks trove of internal emails from officials at the Democratic National Committee was perhaps even more of a kick in the gut, confirming for many Sanders supporters their long-held suspicion that party leaders were plotting against the insurgent campaign.

By late Sunday morning, DNC Chair Debbie Wasserman Schultz had resigned, and a last-ditch effort to prevent nasty displays of party disunity was in full swingParty leaders across the ideological spectrum, including Sanders, were trying to tamp down tensions. But they are still likely to spread onto the convention floor in some form this week, whether in a fight over the party platform and rules, or—as Sanders dissidents are considering—with a Kaine alternative being nominated from the floor.

“We’re supposed to believe that Clinton has been reaching out, evidently she’s reaching out to stick her thumbs in our eyes,” said Norman Solomon, a California-based author and former congressional candidate who is running the Bernie Delegates Network, which has registered 1,250 Sanders delegates to connect and organize at the convention. He said the Kaine pick was being taken as a bad sign of where Clinton was really headed, demonstrating “the limits of what we can achieve. A lot of young people in our state delegation, they’re going to feel like they’ve hit a wall.” 

While many others on the left are ready to take a victory lap of their own in Philadelphia—and then get back to holding Clinton to her promises and completing their ultimate takeover of the party—this frustration over impending betrayal hangs over the opening of this week’s Democratic Convention. The left reaches Philadelphia not only freshly resentful of the party establishment, but divided among itself. 

The events of the past 72 hours not only reignited simmering frustrations; they also complicated the attempts by the most liberal members of Congress, including Ellison and Sanders, to sell a more hopeful message to their ideological soulmates about what they’ve accomplished in 2016, and where the movement that Sanders sparked can go from here. After all, to maximize their influence during a hypothetical Clinton presidency, progressive leaders must have an activist army at their backs. But that army remains unsure of whether to come along.

The glass-half-full case for the left is easy to make. If I had told you a year ago that a self-professed democratic socialist would win 22 states in a presidential primary, raising more money than anyone else in the field in both parties, you would have asked if I’d recently fallen on my head. Bernie Sanders’s campaign “has demonstrated that citizens are ready to put a lot of energy into backing a very different economic structure,” as Jeff Merkley of Oregon, Sanders’s lone endorser among his Senate colleagues, told me last week. The “revolution” has done nothing less than force “a tremendous change in the conversation in what it means to be a Democrat,” added Mark Takano, a second-term representative from California. 

The left looks far more like the party’s future now than it did when Sanders launched his dark-horse bid to shake things up. Younger Democrats, completely unfazed by the specter of “socialism,” flocked to Sanders in the primary contests, giving him more than 70 percent of their votes. Sanders’s success appeared to herald a final, emphatic rejection of any lingering sentiment from the 1990s, the heyday of the Clintonian Democratic Leadership Council (DLC), that Democrats can’t run on straight-up populist and progressive issues and win. The new left was too strong to settle for that anymore. 

Significantly, Clinton had to move left throughout the primaries to fend off Sanders, switching to opposition to the Trans-Pacific Partnership (TPP) trade agreement and the Keystone XL pipeline, among others. For many, that remains a hopeful sign. “She’s proven herself willing to listen,” Ellison said. “There’s a big difference between pandering and listening. You want a politician that listens, you don’t want one that panders.”

Even after Clinton had finally dispatched Sanders, she kept shifting left. Clinton strengthened several of her policy prescriptions to accommodate progressive voters, most notably rolling out a revised plan on college affordability that now guarantees free tuition at public colleges for students whose families make up to $125,000 a year (roughly 80 percent of the population). And the party platform, while leaving out an explicit rejection of TPP or a ban on fracking, has more progressive planks—from endorsing a $15 an hour minimum wage to abolishing the death penalty—than any time in history.

Takano is among those who think it’s time to declare victory and move on. “I think we need to work with the young people who campaigned so passionately for Bernie Sanders and encourage them to celebrate the victories they helped bring about,” he said.

Sanders has been teeing up this shift over the past month. He’s launched two new political organizations: Revolution Now, dedicated to training and recruiting a new generation of progressive candidates from school board and city council on up, and the Sanders Institute, focused on new ideas and public education. The movement works to keep organized the millions of new voters and volunteers who got excited about progressive politics for the first time in 2016—including some less-official, more grassroots-driven efforts hatched at last month’s People’s Summit of 3,000 Bernie-backers in Chicago. It appeared that everyone could come to Philly with warm feelings, though mixed with a touch of Clinton queasiness.

But that was before Friday. 

Tim Kaine’s pick, warmly received by some after his first campaign speech in Miami, landed with a thud among the progressive base. Kaine supported Virginia’s right-to-work law as governor, and offshore drilling in the Atlantic as senator. He was one of 13 Democratic senators to support fast-track trade authority (though he will reportedly now reject the TPP deal). And his experience as DNC chair from 2009-2011, where he raised $229 million and spent three days a week chasing big money, suggests a coziness with the current campaign-finance system—which Sanders and his supporters just happen to see as the core problem with modern politics.

On CNN Sunday, Sanders called Kaine “more conservative than I am,” but added, “on his worst, worst day, 100 times better than Donald Trump will ever be.” Not all of his supporters are feeling so charitable. A survey of more than 250 Sanders delegates by the Bernie Delegate Network before the selection showed that Kaine was only acceptable to 2.7 percent of respondents, and unacceptable to 88.5 percent. In a statement after the announcement, Karen Bernal, a Sanders delegate from California, called the Kaine pick “a big ‘shut up and sit down’ to the progressive wing of the party.” Like other disgruntled Sanders delegates, she saw it as a bad omen about Clinton’s real intentions: “Rather than demonstrate she will work to roll back the worst of neoliberal economic policies, she’s apparently decided to promote them,” Bernal said. 

The displeasure with Kaine could lead to a floor fight, or—more likely—a brief disruption of the party’s smooth show of unity this week. On Sunday, unhappy delegates in the Bernie Delegate Network said they were discussing a range of possibilities: a mass delegate walk-out, an organized back-turning during Kaine’s convention address Wednesday night, or a last-minute effort to gather the 300 signatures necessary (no more than 50 from any state) to put a left-wing alternative into nomination. Former Ohio state Senator Nina Turner has emerged as one potential name. “You might call what’s on the horizon a possible Kaine mutiny,” said Norman Soloman.

That’s overselling it: Even something as dramatic as an alternative nomination is practically certain to end as a symbolic gesture of protest. But unsatisfied Sanders delegates will insist that their voices be heard at the convention, both on the vice-presidential pick and the parts of the platform where they still want the party to take a stronger position. 

“The DNC is the appropriate place to argue out these issues in a democracy,” said Donna Smith, executive director of Progressive Democrats of America, which claims over 220 Sanders delegates as members. “The Clinton team is talking about party unity, but Bernie delegates are isolated.”

The Wikileaks emails only reinforced that sense of alienation for some Sanders backers—proof, to them, that the system really was rigged against their candidate. One email showed DNC staffers musing about how to depict Sanders as an atheist before Southern primaries; others showed Wasserman Schultz referring to Sanders campaign manager Jeff Weaver as a “damn liar,” not to mention an “ASS.” 

Wasserman Schultz’s resignation did not immediately placate angry Sanders backers. “Our election was stolen, rigged, but Debbie Wasserman Schultz is fired so we’re supposed to feel better?” raged Executive Director of National Nurses United Rose Ann DeMoro on Twitter on Sunday.

However much the left’s lingering frustrations and suspicions of Clinton and the Democratic establishment may spill over onto the floor in Philadelphia this week, most of the dissidents will likely come around in November. An election where failure equals the elevation of Donald Trump to the leadership of the free world should concentrate minds nicely. 

But that won’t end the friction. A strong (and young) strain of the left will leave Philadelphia still hesitant about whether to see Clinton—or the party she now controls—as a partner or an adversary. Some may try to build social movement outside of politics, à la Occupy Wall Street. Some may just walk off the political field.

The continuing turmoil certainly threatens the carefully directed efforts by progressive leaders like Sanders and Ellison to motivate the new foot soldiers pouring into their movement, now that there’s no campaign to rally them around. Despite all the leftward advances from Clinton and the party, despite the platform victories and budding plans to build the revolution, will the distaste for party politics linger? 

The Democratic left’s apostles of optimism have a hard sell to make: The remarkable success of Sanders’s campaign has itself made it hard to argue for half-measures and incremental progress. But Ellison and others can point to the ultimate ousting of Wasserman-Shultz as a demonstration of how political fights are often slow and laborious, but occasionally rewarding. And they can point to another victory, during the turmoil of the weekend, when the party’s Rules Committee united to agree to overhaul the superdelegate system. In future primaries, elected officials can still vote for whatever presidential nominee they want, but other superdelegates, like party leaders, will be bound to vote in the same proportion as the results of their state. Even the gloomiest of Sanders supporters expressed contentment. “The compromise on superdelegates might remove the need for a floor fight,” Norman Solomon said.

Ultimately, though, the progressive left will only truly be ascendant if its new base can be coaxed back into battle. Sanders will try to rally the troops in his big speech on Monday night. Meanwhile, allies like Ellison are warming up for the arguments ahead. “If you fight for your principles, you can get successful enough so that even if you don’t win, you can still shape the agenda,” Ellison said. “But if you take the attitude that the system’s corrupt and you check out, then you can’t shape anything. And you basically have to live with what whoever is in power decides to do.”