Bernie Sanders spent the better part of three decades in national politics trying to bring ideas that would strike most of the democratic world as fairly conventional into the mainstream of American politics.

From 1990 through 2015, the congressman-then-senator from Vermont had to content himself with a cult following on the progressive left and a reputation for decency that eludes most politicians. Largely unavailable to him were the conventional tools factional and party leaders use to advance their causes. Sanders was a relatively infrequent guest on national news programs. He seldom campaigned outside his home state for Democrats, and when he did, it wasn’t to a mass of supporters fanning out toward the horizon. 

Sanders’s first fleeting taste of national fame came, as so many moments in the spotlight do these days, on social media, when he protested President Obama’s 2010 decision to temporarily renew regressive George W. Bush-era tax cuts by occupying the Senate floor and delivering an eight-and-a-half hour oratorical remonstration against inequality and oligarchy in America. The performance was a sensation among denizens of the online left, and later became the basis of a book titled The Speech: A Historic Filibuster on Corporate Greed and the Decline of our Middle Class. But by that time, the Bush tax cuts had been extended and Sanders had returned to relative obscurity, resurfacing only once, to promote the idea of a progressive primary challenge ahead of Obama’s re-election campaign. Democrats rebuffed him overwhelmingly.

It’s not that Sanders’s vision for the country was denied a hearing because it was fringe—promoters of ideas far more extreme are received warmly in the media all the time. Sanders wasn’t on the news often because he was often unable to make news. He was a political independent, for one thing. Moreover, activist progressives like him lacked the numbers and organizational prowess to force their ideas on the Democratic Party the way movement conservatives have done to Republicans for decades.

It took a relentless and phenomenally underestimated presidential primary campaign for his message to finally break through to the masses, and as it turns out the receptive audience was enormous. Over the course of a year, Sanders has hosted dozens of rallies the size of small cities, won 19 caucuses and primaries so far in states large and small (with another expected in West Virginia on Tuesday), and compiled a massive list of supporters, comprising millions of people who together donated north of $100 million to his campaign.

But like many insurgents who came before him attempting hostile takeovers—the Eugene McCarthys, Jesse Jacksons, Howard Deans—Sanders is not going to secure the Democratic Party’s presidential nomination. In the near term—between the end of the primaries in June and November 8, 2016—this confronts him with the narrow question of how aggressively and passionately to campaign for the person who beat him. 

But beyond this election, Sanders’ newfound clout will confront him with a much different set of questions, stemming from this basic challenge: How can he continue to harness the enthusiasm that defined his candidacy beyond the time-limited scope of a campaign? How can he avoid the common traps that have ensnared so many other reformers with national followings—like becoming subsumed into the system he wants to change, or allowing the followers he’s nurtured to disengage from politics?

The dream scenario for Sanders Democrats is that he’ll end up, like Barry Goldwater, sparking a movement that eventually comes to dominate his party. The danger is that his challenge to Democratic orthodoxy could end up having no more lasting impact on the party than those of the insurgents who’ve come before him.

There’s a playbook Sanders could follow that would end in tears for his supporters. The Sanders campaign bears more than a passing resemblance to Dean’s, which never translated into anything like the kind of revolution Sanders wants to foster. Though Dean forced a course correction on a Democratic establishment that had become a dangerously pliant enabler of the George W. Bush administration, he only moved his party to the left incrementally. But, happily for Sanders backers, it’s the differences between the Dean and Sanders phenomena that offer hope that the Sanders moment could endure. For his campaign to pay continuous progressive dividends, he will have to exploit the qualities that distinguished his crusade from the crusades of other Democrats.

Dean, it’s important to remember, came to national prominence because congressional Democrats supported the invasion and occupation of Iraq, and had more generally bungled post-September 11 national security politics. His campaign was the first in history to use digital tools to raise money and organize, and might have succeeded had it not been beset by internal dysfunction. But Dean lost the 2004 Democratic primary—to a candidate who had supported the war, no less—and the Dean machine diffused into the liberal ether. That isn’t to say it disappeared, but it became attenuated, thinly spread, and was ultimately largely subsumed into the machine that Sanders now sets up as a foil.

Deaniacs brought scale and professionalism to the grassroots group They worked for progressive candidates and members of Congress. They joined the labor movement. They created a social media and fundraising model that Barack Obama would eventually use to greater effect. And they converted the campaign itself into the advocacy group, Democracy for America, which backs progressive causes and politicians, including Sanders, to this day. But their victories accumulated slowly. In 2006, with Dean chairing the Democratic National Committee, Democrats won the midterm elections in a landslide—a “thumpin’,” as President Bush so memorably described it. And over time, Dean’s critique took hold within his own party, as Democrats began disavowing the war they had helped to start. But the Iraq War persisted through the Bush era, and much of the Obama era, and despite the official termination of Operation Iraqi Freedom, it continues in some ways to this day.  

Here is where the differences begin to pile up. Sanders’s campaign was better-run and more successful than Dean’s. But more critically, its animating cause wasn’t acute or ephemeral like an unjust war. Sanders isn’t a critic of a single, massive policy error, or of liberalism cowering briefly to neoconservatism in the wake of a national panic, but of the very foundation of the American political economy. Sanders seeks nothing less than the wholesale transformation of the Democratic Party into a vessel for social-democratic politics.

Sanders’s critique will continue to appeal to his cohort of liberal supporters—many of whom came of political age amid the devastation of a massive failure of Western capitalism—at least until the economy becomes healthier and more equitable. He built his following through a shared sense that inequality, oligarchy, and income stagnation are moral failings of a corrupt or indifferent political system. The breadth of these injustices will theoretically give Sanders supporters more focal points for activism than Dean’s supporters had. 

But as they grapple with how to prevent the enthusiasm for his candidacy from fizzling out, they will need trusted leadership, and Sanders has been vague about how or whether he will marshal the forces he’s unleashed. The Democratic Party won’t be fully remade in Sanders’s lifetime—he is 74, after all—but it probably won’t happen at all without his early involvement. To succeed where others failed, Sanders can’t simply become a functionary, working to reform the Democratic establishment from within. The inside game will be a big part of the project, but not the only part. Sanders must keep the apparatus he’s built largely intact, but refocused on lobbying for progressive policies and promoting and financing progressive candidates—and making establishment Democrats fear the price of opposing both. Part, channeling grassroots enthusiasm for progressive causes; part Heritage Action, forcing conformity upon Sanders’s party.

Such an operation will lose momentum quickly if Sanders is not its key spokesman and final decision-maker. It will also lose momentum if long stretches of time pass without big progressive causes to champion, and here Sanders can use his status as a sitting senator to his advantage. It is feasible that Democrats will reclaim the Senate in 2016, and if they do, Sanders is in line to chair the Budget Committee, a panel with limited formal jurisdiction, but vast agenda-setting potential. A congressional budget lacks the force of law, but often serves as a statement of the majority party’s governing objectives: Who are we going to tax, how much, and to what end? 

It was from the helm of the House Budget Committee that now-Speaker Paul Ryan was able to rally Republicans around a radical agenda that has formed the basis of nearly every GOP candidate’s platform since its introduction. Should Sanders use his chairmanship in a similar way, he will extend the intra-liberal debate he sparked during the primary about the ideal scope and architecture of social policy into governing season. He’ll keep pressing the question: What should a country provide its citizenry, and should it provide those things to all, or only to some, on the basis of need?

Like a Ryan of the left, Sanders will have an opportunity to cajole (and if need be, push) Democrats in a more progressive direction, but he can also serve as a bulwark against regressive policymaking, the same way conservatives have time and again stopped Republican leaders from consorting with Democrats on any measure that carries a whiff of liberalism. If and when President Clinton forges illiberal compromises with Republican leaders, Sanders will be one of the only people in Congress with a constituency wide enough to make other Democratic members consider rebelling against the leader of their party.

The toughest task for the Sanders movement may ultimately be the most important: finding enough talented progressive politicians to run for office, financing them well enough to compete in the money-drenched world of modern politics, and getting them elected in parts of the country that aren’t already reliably progressive. For Sanders to turn his national constituency into mutable political leverage, he will need acolytes who adhere to fairly strict ideological criterion—and win. The lesson of right-wing Republican politics, from Goldwater to Gingrich to the Tea Party, has been that imposing purity tests on candidates can lead to embarrassing failures (such as the candidacies of Sharron Angle, Christine O’Donnell, and others), but also that fielding ideologically committed candidates can pay huge dividends, both electorally and in expanding the scope of substantive debate. (It isn’t an accident that by today’s standards, Ronald Reagan would be considered a moderate Republican.)

But moving the Democratic Party leftward in a similar way, far beyond the liberalism of Clinton and Obama, will be expensive, and thus require a fundraising machine that picks up where the Sanders campaign leaves off. Money is a foregone conclusion for most conservative candidates. But while Sanders famously proved that millions of people will contribute an average of $27 a pop to finance his campaign, we still don’t know how extensive that largesse really is. How many of those donors have the means to support multiple candidates simultaneously, at a similar level of giving?

The obstacles are considerable, but it is possible to imagine Sanders breaking the mold of previous Democratic insurgents and converting the machine he’s built into a movement whose influence and power nobody questions. Progressives have compiled big lists before, only to be reminded that they are just one faction among many in Democratic politics. Until Sanders came along, they weren’t even a particularly formidable one. We’ll know before too long if that has changed.