As I have noted in previous work, one of the core insights of the Critical Legal Studies movement is that legal positions that at one time would have been considered "off-the-wall" can become mainstream "upon a shift in the direction of political winds (quoting Mark Tushnet, Defending the Indeterminacy Thesis)." I was reminded of this point when reading the Supreme Court's decision in Town of Greece v. Galloway.
I am not a Constitutional Law scholar, and the decision is based on a highly specific set of facts. This being said, one proposition that I would have considered unassailable is that the Federal Government cannot, consistent with the Establishment Clause, designate an official religion. And yet Justice Thomas's concurring opinion (joined by Justice Scalia) states the following:
As an initial matter, the Clause probably prohibits Congress from establishing a national religion (emphasis added).
This statement is followed by a CF cite, indicating that there is only weak support for this proposition.
Based on the foregoing, could attorneys reasonably advise that it is "unsettled" whether Congress can establish a national religion?
Update: As noted by Thomas in the comments, Justice Scalia did not join the part of Justice Thomas's concurring opinion that features the quotation in question. The post has been corrected.