Brandon Johnson, a union organizer and former teacher, was elected as Chicago’s next mayor Tuesday in a major victory for the Democratic Party’s progressive wing as the heavily blue city grapples with high crime and financial challenges.Johnson, a Cook County commissioner endorsed by the Chicago Teachers Union, won a close race over former Chicago schools CEO Paul Vallas, who was backed by the police union. Johnson, 47, will succeed Lori Lightfoot, the first Black woman and first openly gay person to be the …