seoul south korea president moon jae-in say hop visit u.s president donald trump would turn point efforts defuse tensions north korea nuclear program two leaders meet seoul tuesday state visit south korean capital bill opportunity trump moon present unite front despite differences confront north korea nuclear threat well trump complaints two countries trade agreements besides vow prevent north korean leader kim jong un develop nuclear weapons missiles effectively strike mainland unite state trump also threaten pull free trade pact two countries trump visit could 'turning point north korea policy say moon