President Trump signed an executive order declaring a national emergency in the mining industry, ordering the Interior Department to increase domestic production of rare-earth materials to reduce the country’s dependence on China. The order states, “our Nation’s undue reliance on critical minerals, in processed or unprocessed form, from foreign adversaries constitutes an unusual and extraordinary threat, which has its source in substantial part outside the United States, to the national security, foreign policy, and economy of the United States. I hereby declare a national emergency to deal with that threat.” The US imported 80 percent of its rare-earth materials and...