This won't happen. I know that Fox News is screaming that Trump will be stopped, but they are wrong. The Supreme Court has never denied a President the actions that he thought necessary to deal with a National Emergency. The press will get their panties in a wad, but it will not matter.
So one just made that point, on MSNBC!, that Congress gave the National Emergency power to the President in a 1976 act. A future dem president can declare one on guns,but of course, they would do it anyway, and violent war will result.