The First Amendment to the U.S. Constitution begins, "Congress shall make no law respecting an establishment of religion… ." Over the many years in which the Establishment Clause has been at the heart of disputes reaching the U.S. Supreme Court, the court has struggled to pronounce a consistent standard to determine whether the federal government (or now, through the Fourteenth Amendment, a state), has violated the Establishment Clause.

Everyone acknowledges that, for example, Congress may not establish a national religion, as England did with the Anglican Church. Beyond that, though, the justices typically have failed (and continue to fail) to reach unanimity. See, e.g., American Legion v. American Humanist Association, 139 S.Ct. 2067 (2019); Zelman v. Simmons-Harris, 536 U.S. 639 (2002).