After a heated debate, the Caucus Of Rank-and-file Educators (CORE) of the Chicago Teachers Union voted at its February 22, 2016 regular meeting to endorse the candidacy of Bernie Sanders over Hillary Clinton in the March 15, 2015 Democratic Party primary in Illinois. The vote was overwhelming in support of Sanders (this reporter is a member of CORE and was present and voting at the meeting).

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The endorsement vote came in part in response to the fact that for more than six months, the Chicago Teachers Union (and hence all CORE members) had been forced to support the Clinton candidacy. The Executive Council of the American Federation of Teachers (AFT) had endorsed the Clinton candidacy after a controversial "push poll," which AFT President Randi Weingarten tried to characterize as a "survey" of the union's members, hence justifying the early Clinton endorsement.