Not long ago, despite the national AFL-CIO’s decision to hold off on an early endorsement, it looked like organized labor was falling in line behind the establishment candidate for the Democratic nomination. In late July, the American Federation of Teachers (AFT) voted to endorse Hillary Clinton; heavyweights like the National Education Association and AFSCME followed.

The endorsements betrayed a dissonance between labor’s base, which has appeared increasingly willing to confront city and state Democratic establishments, and a national labor bureaucracy loath to take the risks necessary to challenge Washington’s neoliberal consensus.

Bernie Sanders’s support from the National Nurses United, a union with over 180,000 members, was a notable exception, with few other large unions indicating a willingness to make the jump. But last week’s endorsement of Bernie Sanders by the American Postal Workers Union — and its 200,000 members — shows that more segments of the labor movement may be willing to challenge Clinton in the primaries.