Congress shall make no law respecting AN establishment of religion.
It isn't a verbal, it's a noun.
Good catch. Still, it doesn't change the point of my post. To the Founders, "Establishment of religion" meant an official state church. Their intent was to prevent the US from following the custom of the time as in England where membership in the official state church, the Church of England, was required by law under certain circumstances and where legal decisions or an individual's or group's status under the law could be based on church membership.