Without an oversized U.S. presence and role, China’s calculation regarding North Korea might be different. North Korea is a drain on China’s resources. South Korea and Japan are a $200 billion export market for it.

The U.S. position is the fewer nuclear powers in the world the better. So, we extend our nuclear deterrent to allies facing a nuclear threat. We don’t want even more good guys to have nukes.

But making that deterrent credible and unexercised requires us to get involved in virtually any regional dispute involving a nuclear bad guy.

If the United States had more robustly developed missile defense capabilities over the last decade or so, we might be in a position to argue to good guys (or even not so good guys) facing nuclear bad guys that missile defense was a sufficient deterrent. But we’ve slow-walked missile defense development and that’s a claim currently open to doubt.

If bad guys are going to proliferate, and if missile defense provides insufficient assurance, the United States may need to rethink its view that no new good guys, regardless of circumstances, should go nuclear. A nuclear South Korea and Japan would pose no threat to the United States, but it might relieve us of the need to truck with the likes of North Korea.