The issue focused on national security and military needs. The White House said it had done so as part of an effort to improve economic conditions in North Korea.

US political strategists were concerned that President Trump was moving too quickly to pressure Pyongyang. But there is no evidence that he has changed his mind. He now appears less prepared for the prospect of military action.

That political resistance may have played a role in Mr Obama's decision not to send military troops into South Korea. That military presence also meant