For reasons that could range from good to atrocious, U.S. President Donald Trump wants a three-way summit with his Russian and Chinese counterparts when the three men are in Shenzhen next month for an economic forum.

In the worst scenario, Trump and Xi Jinping would conspire to doom Ukraine to Vladimir Putin’s subjugation. In the best, however, they would open a long and necessary process toward an eventual nuclear detente among the U.S., Russia and China. Trump claims he wants this trilateral meeting “not so much for Ukraine” but “to talk about nuclear weapons and denuclearization.” Let’s take him at his word.

What would such talks look like? And what lesson could Trump take from a West German chancellor in the 1970s?