The Room Where It Happened: A White House Memoir by John Bolton:
I left South Korea for Ulan Bator in the early afternoon, watching reports of the events in the DMZ as we flew. As foreshadowed by his earlier comments and the irresistible photo op presented, Trump walked into North Korea, with Kushner and Ivanka nearby. Kim looked delighted in the pictures, as he should have. What an incredible gift Trump had given him, coming to the DMZ for the personal publicity. The whole thing made me ill. It didn’t get better later when the media reported Trump had invited Kim to the White House. The Kim-Trump meeting itself lasted about fifty minutes, and the two leaders agreed working-level talks should resume again quickly. Of course, Biegun did not yet have a new counterpart; his former one was now likely lying somewhere in an unmarked grave, but no matter.