One year ago, Bernie Sanders stood in the sun on the shore of Lake Champlain and opened his presidential campaign with a promise “to build a movement of millions of Americans.” Critics scoffed, dismissing his supporters as callow youngsters destined to drift once #FeelTheBern stops trending. But Sanders’s campaign proved more popular and resilient than anyone expected. Ironically, many Democrats now want him to terminate his movement and convert it into a get-out-the-vote drive for Hillary Clinton.

But that is not how movements work. The celebrated political movements of American history—abolitionism, progressivism, and civil rights—were never subordinate to political parties. Their leaders did not bow to party elites. Great movements transcend partisanship; they are the makers and breakers of parties.

The Democratic Party itself was forged in the fires of populism. Andrew Jackson was a loyal Democratic-Republican senator until party elites blocked his presidential bid in 1824. Denouncing the “corrupt bargain” that thwarted the will of the people, Jackson angrily split with the party and won the presidency four years later as the head of the emerging Democratic Party, while the old Democratic-Republicans disappeared into history. Modern Democrats still honor the party’s mascot, which was inspired by the Democratic-Republicans’ epithet for Andrew Jackson: an ass.

The Republican Party was also born of a grassroots revolt. In 1854, Democratic and Whig legislators passed the bipartisan Kansas–Nebraska Act, which sanctioned slavery in western territories. A few weeks later, thousands of abolitionists gathered beneath a grove of oak trees in Ripon, Wisconsin. Appalled by their respective parties’ accommodations to slavery, they resolved to form a new party dedicated to resisting the spread of slavery. Six years later, the Whigs collapsed, the Democrats split, and a former Whig named Abraham Lincoln became the first Republican president of the United States.

But a movement need not destroy a party to make an impact. The Progressive Movement revolutionized American politics in the early 20th century by putting extraordinary pressure on the Democratic and Republican parties. During the Gilded Age, corrupt political machines fueled by corporate money dominated American politics. As public resentment smoldered, populist insurgents from both parties mounted grassroots campaigns to reform the system and overthrow the establishment. The party bosses fought back, denouncing the insurgents as dangerous demagogues who would plunge the country into economic collapse or worse. Both parties erupted in turmoil.

The chaos came to a head in 1912 when former president Theodore Roosevelt campaigned for the Republican nomination on a progressive platform. Accusing the party bosses of stealing delegates, he bolted the presidential convention to found the Progressive Party, popularly known as the Bull Moose party. Though Roosevelt lost the election, his campaign decimated the conservatives who had obstructed political reform for years, and a bipartisan progressive alliance under Woodrow Wilson fulfilled one of the most ambitious legislative agendas in American history.

America’s landmark civil rights legislation was also the product of heavy political pressure. For decades, northern liberals coexisted uneasily with southern segregationists in the Democratic Party—a coalition of convenience that John F. Kennedy continued to honor after he became president in 1960. When Freedom Riders began challenging segregation on interstate buses, Kennedy regarded them as a nuisance. “Can’t you get your Goddamned friends off those buses?" he complained to a Justice Department official with ties to the movement.

But civil rights leaders carried on. Writing from a Birmingham jail, Martin Luther King Jr. reproached “the white moderate, who is more devoted to ‘order’ than to justice; who prefers a negative peace which is the absence of tension to a positive peace which is the presence of justice.” After Birmingham police turned their dogs and firehoses on peaceful demonstrators, Kennedy and other Democratic leaders could no longer turn a blind eye to the abuses of their southern colleagues. “The events in Birmingham and elsewhere, have so increased the cries for equality that no city or state or legislative body can prudently choose to ignore them,” Kennedy proclaimed on national television. “A great change is at hand, and our task, our obligation, is to make that revolution, that change, peaceful and constructive for all.”

When Bernie Sanders calls for a “revolution” to reform American politics in the 21st century, he aspires to emulate these earthshaking movements that changed history. Such a movement cannot be realized in a single election cycle; it will take years, even decades, to reach maturity. And Sanders need not become president to fulfill it. Some future president who ultimately executes Sanders’s vision would likely be a late convert to the cause, much like Abraham Lincoln, Woodrow Wilson, and JFK.

But if Sanders hopes to see his fledgling movement take flight, he should not subordinate it to the short term electoral interests of the Democratic Party. Like any large institution, the party is subject to inertia; great force is required to redirect its course. If Sanders yields and meekly throws his support to Clinton, the nudge that he gave the party during the 2016 primary race will be for naught. His impassioned supporters will drift away, fulfilling the prophecies of his critics, and the party will roll on as before.

That does not mean that Sanders should throw the election to Donald Trump, who is anathema to his cause and a threat to the nation. But if Sanders hopes to change the Democratic Party, he must take it to the brink. He should run up his delegate count until the final primary and then demand a price for his allegiance: speeches at the convention, planks in the party platform, and progressive voices in Clinton’s cabinet. Above all, he must secure a stable foothold for his emerging faction so that it can grow into the dominant force in the party.

Such negotiations won’t be pretty. The Democratic leadership won’t budge unless they believe that the welfare of the party and the path to the White House are jeopardized. There will be howls of rage, accusations of egotism and demagoguery, just as there were during previous movements. But as they said in Theodore Roosevelt’s time, politics ain’t beanbag. To build a lasting movement that will influence the country for years to come, Sanders must force Clinton and Democratic leaders to reckon with the power of his supporters and bend to their will.

Michael Wolraich is the author of Unreasonable Men: Theodore Roosevelt and the Republican Rebels Who Created Progressive Politics ( one of the Washington Post’s “50 notable works of nonfiction”). He has also contributed to The Daily Beast, Rolling Stone, The Atlantic, New York Magazine, CNN.com, Talking Points Memo, and Reuters.