As Nicholas Eberstadt has noted, the North Koreans are tough, wily negotiators, who use unpredictability as a key tactic. We saw that with the news yesterday that they cancelled high-level talks with the South over joint military exercises with the U.S. and threatened to call off the Kim–Trump summit.
This could be about setting the tempo for the negotiations, demonstrating leverage if we seem to want this summit more than they do, and/or setting up a negotiation over the negotiation. Underlining the latter possibility is the shot a North Korean official took at John Bolton, who is going to be the chief internal Trump administration obstacle to a bad deal. The North Koreans surely would love to try to sideline him.
I would except the summit still to happen and believe it will probably be at least superficially successful — even if Kim is insincere, which I assume, he will want to have a good summit and then string us along, hoping to pocket concessions along the way.
The best posture from Trump here is to avoid any more boastfulness or excitement about the planned summit and revert to his “we’ll see” mode, which he did today.