Certainly the second amendment itself isn't settled, so to speak. The individual right to keep a gun extends back only as far as 2008, which was the first time the the Supreme Court (in Heller) decided that the 2nd amendment does actually protect a citizen's right to gun ownership. Prior to that it was largely viewed (by the Court, certainly not by many individuals) as incorrect that the 2nd amendment does guarantee an individual right to own a gun. But even Heller didn't settle the matter. Just last week there was an interesting appeals court case in CA that sought to answer the question of whether states can set limits on concealed carry. The appeals court said that the CA law requiring citizens to specify a need for a CCW does not violate the 2nd amendment. I'm sure that will be appealed to the Supreme Court, too, but without Scalia, the author of Heller if I'm not mistaken, things could look different. I don't have a firm opinion on guns personally, but just wanted to point out that it's not strictly "rule of law" that prevents Congress from enacting stricter regulations. It seems like they could so almost whatever they wanted short of banning individuals from owning a gun, and that such actions wouldn't necessarily violate the constitution, although any new regulations will almost assuredly be litigated by one side or the other. If nothing else, it's at least fascinating for lay people like me who follow the Court as an interested, though uneducated, observer.