North Korea is making nuclear fuel and building weapons as actively as ever, the publicly available evidence suggests. But he now appears to be borrowing a page from Israel, Pakistan and India: He is keeping quiet about it, conducting no public nuclear demonstrations and creating no crises, allowing Mr. Trump to portray a denuclearization effort as on track…

But even some of the president’s top national security officials privately concede that Mr. Trump’s declaration in June that “there is no longer a nuclear threat” from North Korea was a huge error, because it was taken as a signal by China and Russia that the crisis was over and that they could resume trading with the country.

Current and former intelligence officials say new assessments suggest that Mr. Kim has carefully read Mr. Trump and concluded that as long as the optics are good, and the exchanges between the two leaders are warm, he can hold off demands for progress toward disarmament. If Mr. Kim does not conduct tests, Mr. Trump is unlikely to call out evidence of a continued nuclear buildup.