States can establish religions. Federal government can’t.

Over the last 150 years, the Supreme Court has pretty consistently found that the Bill of Rights applies to state as well as federal government: https://en.m.wikipedia.org/wiki/Incorporation_of_the_Bill_of_Rights

See especially https://en.m.wikipedia.org/wiki/Everson_v._Board_of_Education:

Everson v. Board of Education … was a landmark decision of the United States Supreme Court that applied the Establishment Clause of the First Amendment to state law.