Mexican Finance Minister Arturo Herrera is worried about his country’s sluggish economy. At the International Monetary Fund meetings in Washington in October, he urged Congress to pass the U.S.-Mexico-Canada Agreement to pull his country out of its slump: “It would clearly be an incredible stimulus.”

Mr. Herrera rightly observed that uncertainty is a drag on the economy. But he’s wrong that passing the USMCA—or even preserving the North American Free Trade Agreement—would cure Mexico’s economic anemia. A resolution of the...