California ordered its 40 million residents to stay at home except for essential activities beginning Thursday night in the largest such lockdown in the U.S., as the nation’s total coronavirus cases rose to more than 14,000 and an intensifying outbreak in Europe pushed State Department officials to advise citizens not to travel abroad.

In a letter to President Trump, California Gov. Gavin Newsom said he estimated 56% of the state’s population, or 25.5 million people, would be infected over an eight-week period.

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