SEOUL, South Korea — President Trump arrived in Vietnam on Tuesday to discuss denuclearization with Kim Jong-un, the leader of North Korea, capping off months of threats and weapons tests, recriminations and rapprochements.

As the men prepared to meet for the second time in eight months, their avowed goal of achieving a lasting peace and “complete denuclearization” remained elusive, but the once-imminent threat of war felt even more removed.

Fear of war gripped the Korean Peninsula in 2017 after a series of North Korean missile tests prompted Mr. Trump to threaten that country with “fire and fury.” Mr. Kim responded with what appeared to be a successful test of a hydrogen bomb and launched an intercontinental ballistic missile that it said was powerful enough to reach the continental United States.

After the two leaders met in June, tensions eased dramatically — the North stopped testing weapons, and the United States halted military exercises with the South. But the leaders did not iron out a clear path to denuclearization.