NEW YORK, NY – OCTOBER 08: Democratic nominee for New York Mayor Bill de Blasio (L) appears on stage with current New York Mayor Michael Bloomberg at “CityLab: Urban Solutions to Global Challenges,” an event sponsored by The Atlantic, The Aspen Institute, and Bloomberg Philanthropies on October 8, 2013 in New York City. The event, which took place on October 6-8, brought together 300 global city leaders, city planners, scholars, architects, artists and others for a symposium on urban ideas. (Photo by Spencer Platt/Getty Images)