What was the first case in which “Congress shall make no law…” was interpreted as all levels of government? It looks to me like it was Everson v Board of Education 1947 but I’m looking to see if there was anything earlier.
The concept you’re looking for is called incorporation. According to wikipedia, for the First Amendment, Emerson is it. At least for the Establishment Clause.
Actually, now that I bothered to read the list, there are several earlier cases incorporating other parts of the First Amendment:
Gitlow v. New York (1925) incorporated the freedom of speech part.
Everson. Gotta nitpick. All the kids are doing it.
That’s what I thought but I didn’t want to get it wrong in this discussion I’m having.