The six Republican justices handed down a decision on Friday that effectively legalizes civilian ownership of automatic weapons. All three of the Court’s Democrats dissented. The Court’s decision in Garland v. Cargill involves bump stocks, devices that allow ordinary semiautomatic weapons that can legally be owned by civilians to automatically fire, much like a machine gun designed for that purpose. Bump stocks cause a semiautomatic gun’s trigger to buck against the shooter’s finger, repeatedly “bumping” the trigger and making the gun rapidly fire. A semiautomatic weapon refers to a gun that loads a bullet into the chamber or otherwise prepares...