“There is a grand narrative in the United States that Mexico was the great winner of Nafta,” said Fernando Turner Dávila, the secretary of the economy and labor in the industrial state of Nuevo León. “Meanwhile, here in Mexico, they only see the benefits, which are glorified. They never see the downsides, much less talk about them.”

Mr. Turner cited the loss of nearly two million jobs in the agricultural industry because of the treaty, which benefited highly subsidized industries in the United States like corn to the detriment of Mexican farmers. And while the federal government lauds the increase in manufacturing exports, Mexico still relies on a tremendous number of imports from the United States.

“The Mexican government has not established policies to protect Mexican businesses,” said Mr. Turner, himself a businessman, with factories in a half-dozen countries.

That said, even critics like Mr. Turner do not want to see Nafta gutted. It is an imperfect deal, one that has failed to deliver on its promise, he said. But to terminate the treaty would be a disaster, he said, hurting both Mexico and the United States and creating even more job losses.

It would also not happen easily, critics contend.

After two decades, the two economies are tightly braided together. Goods manufactured by companies operating in both countries — whether speakers, cars or airplanes — cross the border multiple times during production, a shared manufacturing process that, if destroyed, would mean shared job losses.

“A lot of people are taking solace in the reality that it’s very difficult for the U.S. to impose tariffs on Mexico without damaging the U.S. economy as well,” said Christopher Wilson, a scholar at the Woodrow Wilson Institute. “You need something to replace Nafta. Otherwise you’re going to leave a lot of American workers out in the cold.”

The agreement has certainly brought positive changes to Mexico, economists note. Since it went into effect at the beginning of 1994, billions of dollars in investment has been pouring into Mexico every year.