New Delhi, Aug. 18 -- At some point between Saturday's post on social media and Monday's remarks in the Oval Office, Donald Trump said Kim Jong Un sent a response.

"How do you know he hasn't responded?" Asked to be more direct, he was: "Yeah, he has." He described the exchange as "very positive" and said nothing more about its content, its channel, or its timing.

That phrase, "Yeah, he has," is the entirety of what the United States government has publicly confirmed about the state of contact between Washington and Pyongyang as of Monday evening. North Korea has not acknowledged the exchange. South Korea's government, whose military exercises continue despite Trump's reduction order, has expressed hope that the president's personal rapp...