How do you comply with a “stay at home” order if you don’t have a home? That’s a question a growing number of city leaders are grappling with as they ramp up responses to the Covid-19 crisis. And many mayors are taking action with breakneck speed, turning hotels and city-owned buildings into temporary homeless shelters. The reason is simple: The homeless are among the most vulnerable populations when it comes to Covid-19. Many have underlying health conditions and live in close quarters where the virus can spread easily.