SEOUL—South Korea became the first country to successfully negotiate a permanent exemption to new U.S. steel tariffs this weekend in part because the two allies have a bigger challenge ahead: disarming North Korea.
Washington and Seoul had been in the awkward position of scuffling over trade while working toward summits between South Korean President Moon Jae-in and North Korean leader Kim Jong Un, followed by a meeting between Mr. Kim and President Donald Trump.
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