Since Japan already has between nine and 40 tons of weapons grade plutonium (depending on who you talk to, so I’d say the horse is already out of that particular barn.
Plus, it is highly unlikely that Abe is going to listen to anything coming from the Obama administration since it has been policy for at least 30 years to encourage Japan to spend MORE on defense, with a lot of winking and hinting that strategic arms research would not be unduly troubling.
All of this is really a moot point. Japan has undoubtedly produced excellent designs for warheads, has access to all the technology it needs for delivery systems, and I’d bet any amount of money anyone is willing to wager that they have already acquired or prefabricated components — which have been carefully stashed for when they might become necessary.
Japan has bought and paid for a continuous security protective from the US for nearly 70 years. Now it wants a lower US presence on its islands.
Time for Japan to chart its own course.