When Pennsylvania ordered coal mines closed because of the coronavirus, then reversed course and declared them to be “essential,” West Virginia Gov. Jim Justice, who made a fortune in coal, was quick to mock his neighbors. “Coal is so essential it is unbelievable,” said Justice, a Republican. “We have to have good electricity flowing into our homes.” The mine workers union agrees with him. So does President Trump, who has spent the past three years talking up the coal business. But in the face of the pandemic, is coal mining actually so essential? Because of the nature of the work...