A group of Navy SEALs emerged from the ink-black ocean on a winter night in early 2019 and crept to a rocky shore in North Korea. They were on a top secret mission so complex and consequential that everything had to go exactly right. The objective was to plant an electronic device that would let the United States intercept the communications of North Korea’s reclusive leader, Kim Jong-un, amid high-level nuclear talks with President Trump. The mission had the potential to provide the United States with a stream of valuable intelligence. But it meant putting American commandos on North Korean...