It wasn’t President Moon who ultimately broke the war fever. It was Kim Jong Un. First Kim declared his nuclear program “completed” in late November after testing his most sophisticated long-range missile yet. Then, in a New Year’s speech, he proposed sending a North Korean delegation to the Olympics and opening a dialogue to achieve peace on the peninsula, even as he instigated a nuclear button-measuring contest with Donald Trump. Kim’s speech “changed everything,” Chung In Moon said.

The Moon government sprang into action, offering high-level talks within days of Kim’s overture, and began working on a Trump administration that was still very much in a defensive crouch. A critical moment came just a few days after Kim’s address, Chung In Moon told me, when Trump agreed in a phone call with President Moon to “bless” South Korea’s talks with North Korea and accept Moon’s proposal to postpone U.S.-South Korea military exercises until after the Olympics. (During the call, Trump reportedly asked Moon to publicly credit him for forcing North Korea into negotiations, which Moon has since done profusely—repeatedly recommending before the summit collapsed this week that Trump receive the Nobel Peace Prize.) Prior to the call, Chung In Moon recalled, “we [were] all expecting another round of crisis on the Korean peninsula starting from January that could have jeopardized” the Olympics.

As for what motivated Trump’s about-face, it’s an “enigma,” Moon told me, “but we worked hard.” Trump “was quite realistic,” he continued. “On the one hand he was putting pressure on North Korea” with sanctions and military threats, which played a role in Kim’s calculations. “On the other hand he was encouraging President Moon to talk to North Korea.” Trump “deserves credit and recognition for his leadership,” the senior South Korean official told me, particularly for his prioritization of the North Korea issue and mobilization of international support for sanctions.