This post is just a place marker: for the moment, note that a federal District Court in the US has just (on 15 April) struck down a statute providing for a "national day of prayer". I haven't yet read the 66-page opinion of Justice Crabb.
This case should have been a no-brainer - if a statute of this kind is not an unlawful establishment of religion, then I'm going to be the next pope.
Will the US government appeal? I have no idea. But I can't see how an appeal could be successful. Well, um, yes ... I'm afraid I can. It might go all the way to the Supreme Court, which seems like it's itching to craft some kind of de minimis exception so as to save popular forms of "ceremonial deism", such as the words "under God" in the Pledge of Allegiance. This case could be another such example. So, okay, I'm not sticking my neck out and saying that this decision will definitely hold up if appealed.
What I do say is that it ought to stand, as a matter of constitutional principle. Under the US Constitution, Congress has no business enacting a statute that so explicitly endorses a particular kind of religion, in this instance the kind that involves prayers to a God of the sort who listens to them.
Good for the Freedom From Religion Foundation for taking this on. I'll say more when I've read the opinion of the court.