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.