What is the one big thing that could stop Xi, Putin and Trump meeting at Apec?

With just a fortnight until the Apec summit in Shenzhen, preparations are reportedly under way for the first meeting between the leaders of China, Russia and the United States. If the talks go ahead, they could bolster Beijing’s diplomatic standing, although the different priorities of each power were likely to limit consensus and yield few, if any, concrete concessions, observers…