When President Richard M. Nixon met in Beijing almost 50 years ago with Mao Zedong, China’s totalitarian strongman and a nuclear-armed adversary, the two leaders knew they were setting their countries on a new path.

But they had little idea where that path led. They could hardly have foreseen the changes within China or today’s tangled relationship of economic interdependence and intense, if peaceful, rivalry — much less whatever will come after another half century.

Now, it’s President Trump and Kim Jong-un’s turn.

Whether or not they reach agreement on North Korea’s nuclear weapons, the two men appear on their way to the forging the relationship both have said they want. They have portrayed their three meetings — most recently at the Demilitarized Zone dividing the Koreas — as consequential in their own right, loaded with the symbolism of mutual acceptance and respect.

But like Nixon and Mao, the American and North Korean leaders cannot know where their experiment will lead.