Mr. Newsom warned that more than half of California’s population could be infected within eight weeks, but that obviously frightening assertion assumes no social distancing or other precautionary public health measures.

We praised Mr. Cuomo in these pages for pushing back this week against New York City Mayor Bill de Blasio’s suggestion that New York City residents would soon be told to “shelter in place,” which caused panic across the city. Now the Governor has ordered a statewide shutdown that is just short of what Mr. de Blasio suggested.

These shutdowns are extraordinary and have costs, not least the harm to small business owners. Americans may simply decide to ignore the orders after a time. Absent a more thorough explanation of costs and benefits, we doubt these extreme measures will be sustainable for long as the public begins to chafe at the limits and sees the economic consequences.