I'd say there's about 0% chance of using the constitutuon in any defense, if the part you intend to use is the 2nd Ammendment. That silly old thing? Judges have rolled their eyes at Constutional Defense for over a century. And whenever their feet are held to the fire, they find some way to "interpret" it to mean the exact opposite of what is written in very plain and easy to understand language.
Bottom Line: he was arrested for doing something that was illegal according to a law that was illegal itself.
Thus, his action was not illegal and he was arrested for no reason.
But since reality and the letter of the law are not things that any branch of our government abides by anymore; he's screwed.