On a cold day in February 1999, a crowd gathered at Georgetown University to protest the tide of globalization that was reshaping much of the world. Some of their targets, like international trade, might seem familiar today, but the protesters would not have fit in at a Trump rally. They were young and firmly on the left.

Pietra Rivoli, an economist at Georgetown, was watching, and when one woman seized a microphone and, addressing the crowd, asked, accusingly, “Who made your T-shirt?” Professor Rivoli became intrigued. She decided to find out.

She bought a $5.99 T-shirt emblazoned with a colorful parrot in Fort Lauderdale, Fla., and followed its path from Texas cotton fields to Chinese sweatshops and eventually the Walgreens bin in Florida where she had purchased it.

In 2005, she published “The Travels of a T-Shirt in the Global Economy.” Few economics books were as compelling and interesting to me as hers. In a review at the time in The New York Times, I wrote that Professor Rivoli had followed her T-shirt “like Melville followed his whale.” Her tilt was pro-trade and put off by the “moral certainty” of protests, which were erupting against the World Trade Organization in coastal cities like Seattle and Boston.

Professor Rivoli understood the protesters’ concerns about human rights, but did not think shutting down trade would help the intended beneficiaries. A quarter-century later, those left-wing protesters are now middle-aged, and the front lines of the anti-trade movement have passed to the Make America Great Again right, a movement with its own moral certainty.

As President Trump moved forcefully against trade, my thoughts turned increasingly to Professor Rivoli. Now a professor emerita still very much engaged in trade issues, she joked that at least, given the attention that Mr. Trump generated, her students no longer treated her lectures on trade as “nap time.”