1) Haynes and the Fifth Amendment go together in this. First of all, for a long time, I've thought that Haynes was a convicted felon. Looking at that decision now, I don't actually find that fact. I may just be overlooking it, or maybe memory played tricks on me. Nonetheless, he was charged with three counts, which included knowingly possessing an unregistered short-barreled shotgun. SCOTUS framed the issues this way: "The questions necessary for decision art two: first, whether petitioner's conviction under s 5851 is meaningfully distinguishable from a conviction under s 5841 for failure to register possession of a firearm; and second, if it is not, whether satisfaction of petitioner's obligation to register under s 5841 would have compelled him to provide information incriminating to himself." In other words, Haynes was in possession of a short-barrelled shotgun, which was unregistered at the time of possession. He was charged with possessing an unregistered shotgun and failure to register same. The question before the court was whether forcing him to register when he was already in violation of the law would violate his Fifth Amendment privilege against self-incrimination. SCOTUS held that because the registration requirement provided a basis for a real and appreciable risk of prosecution based on self-incriminating information provided by Haynes, "a proper claim of the constitutional privilege against self-incrimination provides a full defense to prosecutions either for failure to register a firearm under s 5841 or for possession of an unregistered firearm under s 5851." Following that logic, a felon currently in possession of a firearm may not, consistent with constitutional protections, be required to register same, or to undergo a background check for a transfer, as the process would require both individual identification (name, address, etc.), as well as disclosure that one had been convicted of a felony.
Source: Haynes v. United States, 390 U.S. 85, 88 S. Ct. 722, 19 L. Ed. 2d 923 (1968).
Spats Cautionary Caveat: Do NOT take this as license to go possess an NFA item, fail to register it and claim protection under Haynes.
2) The Eighth Amendment provides protections from prosecutions for the mentally ill under certain circumstances. If a defendant is charged with a firearms charge and shows some indication of mental illness, just how long do you think it will take his attorney that the mental illness might protect his client?