The administration’s argument has now changed. Should Mr. Kim resume tests, American officials say, it will be a sign that he truly feels jammed, and has concluded Washington will not lift crushing sanctions on his impoverished nation anytime soon.

Left unaddressed, however, is the challenge that a new missile test would represent, and what that would mean for the sanctions strategy. Over the past week, Stephen E. Biegun, the North Korea envoy who was confirmed by the Senate on Thursday as the next deputy secretary of state, has traveled across East Asia to also try to stem new efforts by Russia and China to weaken those sanctions.

Military officials say there are no plans to try to destroy a missile on the launchpad, or intercept it in the atmosphere — steps both Presidents George W. Bush and Barack Obama considered, and rejected. It is unclear if the military’s Cyber Command is still trying to sabotage the launches from afar, as it did under the Obama administration, with mixed results.

Instead, officials say, if the North resumes its missile tests, the Trump administration will turn to allies and again lobby the United Nations Security Council for tightened sanctions — a strategy that has been tried for two decades.

Beneath the recent threats is the onset of a cold reality: In the 18 months after Mr. Trump and Mr. Kim first met in Singapore, with declarations of warmth not seen since the suspension of the Korean War in 1953, the North has bolstered its arsenal of missiles and its stockpile of bomb-ready nuclear material.