Why would the U.S. increase the cost and difficulty of supplying protective gear to doctors and nurses? Why would Washington obstruct the acquisition of lifesaving equipment? Because the sclerosis of trade protectionism, once it takes hold, constricts economic health and adaptation.

Chad Bown of the Peterson Institute for International Economics calculates that the Trump administration has imposed new taxes on almost $5 billion of medical exports from China, totaling about 26% of U.S. health-care imports. With tariffs, the...