The on-again, off-again US-Iran peace talks are casting doubt on whether Donald Trump will make his planned visit to Beijing in a few weeks, though the war could raise the diplomatic stakes of the trip if it does go ahead, Chinese observers say.Hours before a two-week ceasefire was set to end, the US president announced on Tuesday that he was prolonging the fragile truce with Iran.That came after Vice-President J.D. Vance’s trip to Pakistan for a second round of peace negotiations was first...