Sooner or later, and the later the better, the president’s wandering attention will flit, however briefly, to the subject of trade. So, let us try to think about the problem as he seems to: Wily cosmopolitans beyond our borders are insinuating across our borders goods that Americans, perhaps misled by British economist David Ricardo, persist in purchasing.

Exactly 200 years ago, Ricardo published “On the Principles of Political Economy and Taxation,” explaining the doctrine of comparative advantage. Paul Samuelson, a leading 20th-century economist, cited this doctrine when challenged to name a social-science proposition that is both true and not obvious.

Seven years after Ricardo’s book appeared, Thomas Babington Macaulay wrote, “Free trade, one of the greatest blessings which a government can confer on a people, is in almost every country unpopular.” It certainly is with the Trump administration, which bristles with chest-thumping anti-cosmopolitans who are too flinty to be bamboozled by foreigners like Ricardo and others who deny that trade is a zero-sum game.

Foreigners, however, have their uses. After the president trumpeted that the Dow surpassing the 22,000 mark was evidence of America’s resurgent greatness, The Wall Street Journal rather impertinently noted this: Boeing, whose shares have gained 50 percent this year and which accounted for 563 of the more than 2,000 points the Dow had gained this year en route to 22,000, makes about 60 percent of its sales overseas. Boeing has a backlog of orders for 5,705 planes, 75 percent going outside North America. For Apple, the second-biggest contributor (283 points) to this year’s Dow gain at that point, foreign sales are two-thirds of its total sales. Foreign sales are also two-thirds of the sales of McDonald’s, the third-biggest contributor (239 points).

Mark Perry of the American Enterprise Institute says that in the last 20 years the inflation-adjusted value of U.S. manufacturing output has increased 40 percent even though — actually, partly because — U.S. factory employment decreased 5.1 million jobs (29 percent). Manufacturing’s share of GDP is almost unchanged since 1960. Increased productivity is the reason there can be quadrupled output from the same number of workers. According to one study, 88 percent of manufacturing job losses are the result of improved productivity.

But those Democrats who think government should fine-tune everything are natural protectionists and probably think Trump is too fainthearted because he is not protecting Americans from competition from Americans. This neglect might be changing, thanks to West Virginia’s Gov. Jim Justice.

It was beguilingly transactional when Justice recently had his road-to-Damascus moment. Elected as a Democrat nine months ago, Justice, a billionaire from the coal industry, announced at a Donald Trump rally that he had discovered that he is a Republican. Almost simultaneously, he asked for a $4.5 billion subsidy for the coal industry: Taxpayers everywhere should pay Eastern utilities $15 for every ton of Central or Northern Appalachian coal they burn. Naturally, Justice said this is necessary for “national security,” the hitherto neglected menace being this:

Competition from more productive American mines and, even worse, from American fracking is endangering America by threatening the “survivability” of America’s Eastern coalfields, potentially putting America “at risk beyond belief.” Suppose, Justice says, terrorists disrupted the Eastern power grid and there were no abundant supplies of Eastern coal? (He did not explain how the coal would fix the grid.) So, channeling George Orwell, Justice says the subsidy is not a subsidy, it is a “Homeland Security incentive.”

Trump surely will make a similar claim when he proposes to tax Americans (they will pay all tariffs) who jeopardize America’s security by buying American refrigerators made with steel imports that delight America’s circling enemies by putting domestic steel mills “at risk.” Anyone who cannot make a similar argument against imports of Greek yogurt — “food security equals national security” — is a novice protectionist.

George Will is a columnist with The Washington Post Writers Group.