Ald. Deb Mell (33) announced she will not challenge the results of the April 2 runoff, ensuring that six members of the Democratic Socialists of America will join the City Council May 20 — and ending the 44-year span of the Mell political dynasty. Chicago Teachers Union leaders Monday called for a mediator to be brought in to help negotiations, after Mayor-elect Lori Lightfoot called for changes to the timetable agreed to by Mayor Rahm Emanuel.