Support for free trade has ebbed and flowed in cycles that frequently track the ups and downs of national economies. Nearly every political leader is in favor of it or at least claims to be. Yet free trade is under frequent attack these days, and part of the problem is how it is defined.The 2016 G20 summit, a meeting of leaders from the world’s largest economies, will occur this weekend in Hangzhou, China. As this year’s host, China has set the agenda, which includes a discussion of steps to make the world’s economy “interactive, invigorated, interconnected and inclusive.” Generally speaking, various versions of similar objectives have been the goal of these gatherings since the first one convened in 2008 in response to the then-building wo...