Well you have a right to 7 kg of uranium, so if you can find a willing collaborator, you could get 14 kg of uranium.
If enriched, that is enough fissile material for a tactical nuclear weapon, and a destructive device license for the detonator, which would be basic TNT.
It is physically possible for someone to build a legal private tactical nuclear weapon and defend that right in the Supreme Court, just never been done before.
EDIT:
The biggest hurdle is creating highly enriched weapons grade uranium at around 85% U-235, then safely assembling it into the detonator and casing.
It works like a gun, not as crazy or complex as you would think. You slam one piece of fissile material into another with a conventional explosive.
With enough force, basically slamming subcritical material together with TNT like a gun, a nuclear reaction and explosion is initiated.
And now you know, and knowing is half the battle. You can go and make your 2nd Amendment suitcase nuke dreams a reality.