OSAN, South Korea (Reuters) - U.S. President Donald Trump landed in South Korea on Tuesday, the second leg of his 12-day Asia trip dominated by the North Korean nuclear standoff. South Koreans are bracing for the possibility that Trump s state visit could risk further inflaming tensions with North Korean leader Kim Jong Un, who has stepped up his pursuit of nuclear weapons that could soon be capable of striking the mainland United States.  Trump will visit with U.S troops and is also expected to raise criticisms of a U.S-South Korean trade pact when he meets with President Moon Jae-in in Seoul. 