The Pentagon’s investment in MP Materials marked the biggest U.S. intervention in the rare earth industry in decades. The deal established a domestic champion for one of the world’s most strategically important supply chains and demonstrated that Washington is prepared to commit federal financial resources to critical mineral production. Mountain Pass is the only large-scale rare earth mine operating in the United States and one of the world’s largest producers of light rare earths. Its ore is rich in neodymium and praseodymium…