The US somehow has a deal to defend SK. It is on.

with South Korea since the 1950s.

My impression was that the peace "settlement" in the 1950s was a truce, not an official end to the war.

There has been an uneasy truce.

The negotiations at Panmunjom finally bore fruit in 1953 and an armistice went into effect on July 27. Though fighting ended, no formal peace treaty was concluded. Instead, both sides agreed to the creation of a demilitarized zone along the front. Approximately 250 miles along and 2.5 miles wide, it remains one of the most heavily militarized borders in the world with both sides manning their respective defenses. Casualties in the fighting numbered around 778,000 for UN/South Korean forces, while North Korea and China suffered around 1.1 to 1.5 million. In the wake of the conflict, South Korea developed one of the world's strongest economies while North Korea remains an isolated pariah state.

Hell, he lost that before he ever took the oath of office.

He has no global authority. He's made the US the laughing stock of the world.