Give it to them and let them fight it out. No dog in that fight.
Depending on where the (Northern) Polar Jet Stream is at, at the time of the fight, you may have to re-evaluate that. This especially if the situation “builds” such that more than a handful of nukes are involved, and / or China and Japan get involved.
Even now, if you eat a fish out of a body of water in the US not contaminated by a local source, most of the mercury in that fish is likely to have drifted here from China, via much less efficient transport.
All the above does not consider the Nork’s developing missile capacity, and the possibility (I’d call it a likelihood) that under duress, they might do something “nuts”. Yes, the Norks are mostly blackmailers, but, still...
I refer you to: http://www.nti.org/learn/countries/north-korea/delivery-systems/
In which I find the most important bit of information to be: “This prompt sequence of development is remarkable, and historically unprecedented for a small developing country.”