As the summit between Chinese President Xi Jinping and US President Donald Trump fades in the rear-view mirror, marked by anaemic deliverables, poor transparency and missed opportunities, analysts and former US officials point to another disappointment: the world’s most consequential relationship has become inordinately dependent on the two nations’ top leaders. Trump’s May China trip, the first by a US president in nearly a decade, produced vague and contradictory readouts, puffed up promises,...