At least Pres. Trump got to meet with Kim Jong Un to start the discussion. Trump is the first American president to visit North Korea. That is more than any of his predecessors have been able to. Whether or not we like a dictator doesn't matter. When a dictator has nuclear weapons and is building missiles that can deliver them to Phoenix, AZ we need to be talking with him.
For the record the Korean War is not over. In 1953 we signed a truce with North Korea. A truce does not end a war, a peace treaty does.
I'd be cautious about the "able to" part because both the Clinton,
Bush and Obama White House were all invited, and they wisely decided against it.
Both Clinton and Carter HAVE in fact visited but after they left office.