The Bernie Sanders campaign has injected socialism into the mainstream discourse for the first time in decades. Young Sanderistas have rallied behind social-democratic demands that fly in the face of forty years of neoliberal policy, and polls show that millennials are surprisingly receptive to socialist ideas.

The positive response to Sanders’s avowed democratic socialism — and to his call for a political revolution — opens the door for a discussion all but absent from today’s labor movement: the importance of socialist ideas to a successful trade union movement.

For most of the labor movement’s history, a broad socialist-minded wing fused its vision of society with a practical program for labor’s future. Whether it was the industrial unionism of the early 1900s, the CIO unions of the 1930s, or the rank-and-file anti-concession movement of the 1970s and 1980s, labor’s left offered an alternative to union decline and stagnation.