The second amendment states "A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed." Since countries represent people, it is clear that it is a violation of the second amendment to take steps, diplomatic or otherwise, that would infringe on their rights to possess nuclear weapons or the means to create them.
In the last 10 years, the number of deaths due to nuclear weapons has dropped dramatically, so it is clear that nuclear weapons do not cause violence. They provide for self-defense; if one country taxes imports from another, the other can drop a bomb on it.
Other countries like Russia already have nuclear weapons, so efforts trying to prevent further proliferation will be ineffective.