When Donald Trump and Xi Jinping meet Saturday evening on the sidelines of the G20 summit in Buenos Aires, they will do so without illusions. The two most powerful countries in the world are adversaries now, each shorn of any hope that they could somehow be “partners for prosperity” in the 21st century, as the George W. Bush administration used to put it as the century began. The Trump administration stated as much in its formal “national security strategy” released early this year. In a bellicose speech on October 4, Vice President Mike Pence said any American hopes that “economic liberalization would bring China into greater partnership with us and with the world”—the central underpinning of Washington’s strategy toward Beijing since the late 1970s—was now gone. “Instead, China has chosen economic aggression, which has in turn emboldened its growing military,” Pence said.