This term the Supreme Court will hear four consolidated cases challenging the Environmental Protection Agency’s power to regulate greenhouse gas emissions from power plants. That question will impact all electricity consumers, but the cases may have larger implications for the ever-expanding reach of the administrative state. The lead case—West Virginia v. EPA—questions the constitutionality of an ancillary provision of the Clean Air Act that, according to a divided panel of the U.S. Court of Appeals for the D.C. Circuit, gives the EPA broad power to regulate almost any part of the economy that produces greenhouse gases. Joining West Virginia are...