The strange thing there is that for a few decades now federal courts have required a plaintiff to have suffered some sort of injury before they can sue, and the notion that a credible threat is equivalent to such injury seems to overstretch that concept.
Also, the ‘credible threat’ of being prosecuted was based on the agency simply declining to state that it would not sue if Smith violated the law. Seeing as no such violation of the law had even been alleged, it seems incredibly flimsy to say there was a threat at all, let alone a credible threat.
https://harvardlawreview.org/print/vol-136/standing-in-the-w...