The Chicago Teachers Union’s (CTU) internal election is this week. Internal union elections don’t usually draw much attention, but this one is important: the incumbent slate is the Caucus of Rank-and-File Educators (CORE). CORE is the caucus of former CTU president Karen Lewis and other left militants who took over the leadership in 2010 promising to remake it into a fighting force. In 2012, CORE took the CTU into a major strike that made the union the most powerful workers’ institution in the city.

That transformation has had detractors. CORE, whose slate is headed by current union president Jesse Sharkey and Vice President Stacy Davis Gates, is up against a slate called Members First (MF), which argues against CORE’s style of militant unionism on behalf of the city’s entire working class in favor of a more conservative, bread-and-butter unionism.

Those who want working-class power in Chicago and militant teachers unionism across the country to keep growing should hope for a CORE victory on May 17. To understand why, we can take stock of CORE’s achievements in office.