SEOUL (Reuters) - South Korea President Moon Jae-in said he hoped a visit by U.S President Donald Trump would be a turning point in efforts to defuse tensions over North Korea s nuclear program as the two leaders met in Seoul on Tuesday. The state visit in the South Korean capital was billed as an opportunity for Trump and Moon to present a united front, despite differences over how to confront North Korea s nuclear threat, as well as Trump s complaints over the two countries  trade agreements. Besides vowing to prevent North Korean leader Kim Jong Un from developing nuclear weapons and missiles that can effectively strike the mainland United States, Trump has also threatened to pull out of a free trade pact between the two countries. 