U.S. fears Kim Jong Un plans to "give a little, gain a lot"

Even China, which is accustomed to controlling its relationship with North Korea without interference from other powers, is chafing at the speed of events, and the increasingly warm feelings between Pyongyang and Washington. Chinese officials fear that they will be sidelined in negotiations and that Mr. Kim will pursue a deal with the United States that places the North closer to Washington than Beijing.

Much of the anxiety in Tokyo and Beijing stems from the unpredictability of the main players. Mr. Trump, who threatened in August to rain “fire and fury” on the North, is now talking about “good will” between Washington and Pyongyang. Mr. Kim has proved more adroit than many expected in orchestrating the diplomatic opening to South Korea and the United States.

“They’re doing a great job of appearing reasonable, but picking apart the maximum pressure campaign, and positioning themselves to be accepted as a nuclear weapons state in the future,” said Evan S. Medeiros, a former senior Asia adviser to President Barack Obama.