[Sir Francis Dashwood]

It was landmark U.S. Supreme Court precedent Reynolds v. United States in 1878 that made “separation of church and state” a dubiously legitimate point of case law, but more importantly; it confirmed the Constitutionality in statutory regulation of marriage practices.

[BCrago66]

That’s not on point. Legally, marriage in America is not inherently a religious institution. A couple atheists can - in all 50 States - get married by a state official, no ceremony and no sanction from any clergy required.