Thursday morning, the Supreme Court ruled 7-2 in American Legion v. American Humanist Association that a 100-year-old World War I memorial cross in Bladensburg, Maryland, doesn’t “establish” religion. That’s the correct result (read my brief for Cato), but the mish-mash of opinions—it took a paragraph to explain which justice was joining which aspect of the decision—leaves Establishment Clause jurisprudence in the muddled state it’s been for decades.That is, much like in the Ten Commandments cases of 2005, the cross here survived largely because it’s really, really old. Justice Samuel Alito, joined in full by Chief Justice John Roberts and...