Language Log: Under God an Idiom?: "It seems to me that there are only two possibilities here. One is that under God is compositional and has one of the several meanings in which it presupposes the existence of a single deity. In this case, it is unconstitutional. The alternative is that it is an idiom, created at the time it was added to the Pledge, whose meaning we really don't know. I find that highly implausible, because it means either that the people who proposed the addition and the legislators who voted for it didn't know what it meant or that they knew but have somehow failed to pass this information on to us. Furthermore, it's hard to believe that so many people would care so much about retaining it if it had no meaning. Indeed, if its meaning is really unknown, given that the campaign to insert it was led by the Knights of Columbus, we wouldn't expect such strong support from evangelical Protestants for retaining it. Instead, I would expect indifference from some and support for removing it from others, who would see it as a Papist plot, probably with a Satanic meaning. In any case, if it really is an idiom of unknown meaning, it may not be unconstitional, but it has no place in the Pledge because it is meaningless."

Suppose the Iranian Constitution contained the phrases "One nation, under Allah." Would anyone be arguing about what that meant? Nunberg's argument that it is an idiom or a phrase of indeterminate meaning seems implausible on its face, so I agree with post by Bill Poser from which I just quoted.