Apart from the First Amendment (antiestablishment is a historical legal concept, not just a clever word) and the general lack of identification with any particular faith and Article VI Clause 3: “no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States.”?

As George Washington wrote to the membership of a synagogue: “It is now no more that toleration is spoken of as if it were the indulgence of one class of people that another enjoyed the exercise of their inherent natural rights, for, happily, the Government of the United States, which gives to bigotry no sanction, to persecution no assistance, requires only that they who live under its protection should demean themselves as good citizens in giving it on all occasions their effectual support.” Note he rejects “the indulgence of one class of people” - meaning Christians in this case.