The last five years have seen the much-heralded reemergence of the American left. But beyond this period’s big marches and rallies, recent social movements have not been especially welcoming to those not already at least loosely connected to activist networks.

Events like the People’s Climate March and the large Occupy mobilizations brought out hundreds of thousands. But these movements struggled to retain many of the ordinary people who joined them at the peak of their popularity.

Following the Left’s post-Bush-era resurgence, the Sanders campaign has offered an unlikely antidote. Bringing longtime organizers together with new democratic-socialist converts, it has combined its impressive grassroots strategy with a left project that wants to contest for the highest levels of power.