After its charm offensive at the Olympics, North Korea’s delegation has returned home from South Korea, leaving some questions behind. Chief among them: Can the new opening between the two Koreas, begun amid the feel-good spirit of the Winter Games, be nudged and nurtured into serious dialogue over North Korea’s nuclear program?

While still a long shot, there’s a somewhat better chance of engagement now owing to two developments since President Moon Jae-in of South Korea, Vice President Mike Pence, Prime Minister Shinzo Abe of Japan and the North Korean delegation, including Kim Yo-jong, the only sister of the North Korean leader Kim Jong-un, attended the Olympic opening ceremony.

First was Mr. Kim’s surprise decision to dispatch his sister, his most trusted envoy, to carry his personal invitation for Mr. Moon to join him in a summit meeting in the North. Mr. Moon and Ms. Kim met four times during the Olympics, the highest-level contact between the two Koreas in years. Mr. Moon’s visit would be an even rarer event, since the reclusive Mr. Kim has never met another foreign leader.

While many officials fear that North Korea’s primary goal is to drive a wedge between South Korea, which has been eager to engage the North, and the United States, which has resisted engagement, close coordination between Washington and Seoul would keep the alliance strong.