Furious city teachers are threatening to pull their cash from the United Federation of Teachers’ political activities fund after union leaders blindsided them and endorsed socialist Zohran Mamdani, The Post has learned. UFT President Mike Mulgrew and his top allies infuriated rank-and-file members Tuesday by pushing through a resolution to back Mamdani for mayor — approved by 63% of more than 1,000 delegates — with the vast majority of teachers on summer recess and caught off guard. A day after the endorsement, 90 educators vented their anger during a Zoom meeting held by the United Jewish Teachers and NYC Public...