Photo: Michael Nagle/Bloomberg/Getty Images Mayor Mamdani needs to listen to the grumbling members of the political class who are upset that he has not named a deputy mayor who is African American . Whether or not he makes such an appointment, Mamdani should understand the roots of that criticism. It is not simply about one person in one position — rather, the complaints spring from a deep worry about a decades-long mass exodus of Black families out of New York. A tectonic demographic shift is