The sister of North Korea’s dictator was a media sensation—but a diplomatic failure.

The toughest event at this year’s Winter Olympics has turned out to be the diplomatic lunge. Kim Yo Jong, sister of North Korea’s ruthless dictator, emerged as the early favorite, dazzling her hosts and earning points for inviting South Korea’s President Moon Jae-in to visit Pyongyang. The media went into full fanboy mode, giving Ms. Kim the best publicity since Vogue magazine gushed in 2011 that Bashar al-Assad’s wife was “the freshest and most magnetic of first ladies . . . a thin, long-limbed beauty with a trained analytic mind.” In contrast, a dour Mike Pence not only avoided Ms. Kim during Friday’s opening ceremonies but did not stand when the “united” Korean athletic team was introduced, which angered some South Koreans. The Trump administration has assiduously worked to isolate North Korea; is Ms. Kim’s charm offensive now driving a wedge between the U.S. and the South? The answer, at least for now, turns out to be no. In the past, South Korean presidents who jumped at North Korean offers of talks and exchanges ended up suffering political consequences when Pyongyang failed to follow up with real concessions. Moon Jae-in was too smart and too cautious to take the bait. Rather than accepting the invitation to Pyongyang, he urged the Kim regime to talk directly with the U.S.

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