• A week of threatening exchanges between the U.S. and North Korea left China and South Korea on the sidelines and the North Korean leader, Kim Jong-un, effectively in his preferred position: dealing directly with the U.S. Above, Mr. Kim’s image on TV in Seoul on Friday.

Over the weekend, American warplanes flew close to North Korea’s coast, and Pyongyang held a large anti-U.S. demonstration.

We assessed the likelihood that North Korea could, or would, follow through on its threat to detonate a hydrogen bomb over the Pacific.