CHICAGO — On Mayor Brandon Johnson’s first full day in office, he visited ground zero of the crisis that would come to define his next seven months. Striding into the 12th District Chicago police station on the Near West Sidein May, the new chief executive clasped his hands before his waist as he surveyed a lobby floor cluttered with sleeping bags and families of bleary-eyed migrants. “How do you like Chicago so far?” Johnson asked a woman and boy, with political ally andlocal Alderman Byron Sigcho-Lopez, 25th, translating in Spanish. As an aide implored TV news crewsto step back, the mayor co…