washington trump administration plan name washington-based academic former white house official victor cha next u.s. ambassador south korea administration official say tuesday cha former director asian affairs white house national security council serve deputy head u.s. delegation multilateral talk north korea nuclear program administration president george w. bush administration official say expect appointment subject senate confirmation hear announce soon add work long time move come president donald trump face perhaps big foreign policy challenge north korea pursuit nuclear-tipped missile capable hit unite state cha korean american replace mark lippert political appointee serve seoul obama administration cha respond request comment currently korea chair washington center strategic international study director asian study georgetown university department government school foreign service op-ed publish washington post july cha call new approach diplomacy towards north korea argue china must central part future negotiations pay pyongyang halt roll back nuclear missile program south korea long-time u.s. treaty ally trump plan name former bush staffer cha seoul envoy