There are three negative supply shocks that could trigger a global recession by 2020. All of them reflect political factors affecting international relations, two involve China, and the United States is at the center of each. Moreover, none of them is amenable to the traditional tools of countercyclical macroeconomic policy. The first potential shock stems from the Sino-American trade and currency war, which escalated earlier this month when President Donald Trump’s administration threatened additional tariffs on Chinese exports, and formally labeled China a currency manipulator. The second concerns the slow-brewing cold war between the U.S. and China over technology. In...