It is illegal to both posses nuclear materials (U.S. Code § 831) and to "develop or possess a radiological weapon" (U.S. Code § 832)
OK but now that I have made the bomb before you were able to stop me, will the federal government finally recognize Petoria?
The point being made is that if you have enough Nukes you can just tell the US "I don't like Codes 831 and 832, change them or I'll wipe your country out"