Donald Trump is making the first US presidential visit to China in almost a decade, at a time when an increasingly drawn-out conflict with Iran is hammering his approval ratings at home and leaving the Republican desperate for a visible foreign policy win. It wasn’t supposed to be this way. Trump pushed back this summit from a planned date in late March to a time when the White House assumed its brief “excursion” in the Middle East would be over, allowing the Americans to negotiate from a position of strength. Instead, the US seems no closer to wrapping up the war with Iran , and it is China that has come out of the situation looking like a beacon of stability, with its close ally Tehran still standing and its economy largely shielded from the global fallout of the Strait of Hormuz’s closure. The Iran conflict is expected to feature prominently in the discussions between Trump and China’s Xi Jinping – and no doubt be a source of contention.…