JTO,
Indeed, you are right about "shifting the focus". Though this NK ugly shorty would unlikely threaten the US territory, Japan and South Korea are under threat.
But is it really difficult to make VX on a country level? I am not an expert in chemistry, but using a common sense: it was developed in mid 50's in UK by the guys working for agriculture to fight weeds :-) No serious MoD investment, no huge plants in their possession. There was even an open GB patent with all the formulas, reaction chain description, etc. Might be impossible to make for jihadists hiding in the holes, but not for a militarized economy of the 25 mln country.
IMHO, helas, it is only China that can change all that (the NK regime), in a "couple of clicks". But they obviously do not want to: no need for them to scare their long-term rival (Japan) themselves. Let Kim do that.