I thought this opinion piece in Washington Post from last October did a pretty good job of answering that question. The article points out that previous very progressive presidential candidates (i.e. Jesse Jackson’s Rainbow Coalition in the ’80s, which featured significant participation by former hardcore Marxist-Leninist groups) failed to translate their campaign into a longer-term movement, and the volunteer energy fizzled away after election season was over. The only way that such campaigns can translate into real movements, the article argues, is for volunteers to create their own, independent organizations.
But forging a movement from a campaign, and building it in tandem with the many progressive constituencies that for any number of reasons have not flocked to Sanders’s standard and are not likely to — that’s the hard part. Devilishly hard.
This formidable task requires, first, that Sanders’s legions understand the unique historic opportunity that their coming together presents: That their victory in all probability won’t be putting Bernie in the White House, but creating a surging and enduring left. That, in turn, requires them to give as much thought to forming or joining autonomous post-campaign organizations, and envisioning post-campaign mobilizations, as they now do to advancing Sanders’s candidacy. Indeed, they need to start forming such organizations today, while they are together campaigning for Sanders, and in the process even reach out to other progressives who may not be for Sanders. These endeavors can’t and shouldn’t be undertaken by the Sanders campaign itself. They fall exclusively to the volunteers.
Unfortunately, its not clear whether Sanderistas will be able to put thought and energy into forming “autonomous post-campaign organizations” while the campaign is running hot; nor is it clear how many Sanderistas do actually see the campaign as a potential to build a larger movement, rather than a one-off chance to elect a progressive Messiah.
More difficult is the question of what more radical leftists (Marxists, socialists, anarchists, etc.) ought to be doing. What would have been ideal is if we had strong, vibrant organizations that could reach out and relate to Sanderistas for recruitment or coalition-building; but as it stands, the radical left is in even worse shape than America’s social democrats, and existing radical organizations that try to absorb an influx of Sanderistas will likely turn into social democratic organizations themselves, rather than act as a radicalizing pole.