Nina Hachigian: What joins the United States and China and what divides them?

  Next week, President Barack Obama and Chinese President Xi Jinping will meet on the sidelines of the third Nuclear Security Summit in the Netherlands. The summit will highlight an issue on which the United States and China have cooperated to a degree in the past: nuclear proliferation. But the bilateral meeting will also cover more touchy subjects, including the current crisis in Ukraine, cyber theft, and regional territorial disputes. Such is the ever-dual nature of U.S.-China relations in the modern era.