American corn shipments to Mexico totaled nearly $2.6 billion last year and are part of a complex agricultural trade relationship between the two nations that has helped interlace their economies. Though the corn business is a tiny fraction of the overall $525 billion in annual trade between the two countries, it has gained outsized importance and become something of a symbol for the nations' economic co-dependence.
The prospect that the United States could lose its largest foreign market for corn and other key products has shaken farming communities throughout the Midwest, where corn production is a vital part of the economy. The threat is particularly unsettling for many residents of the Corn Belt because much of the region voted overwhelmingly for Trump in the presidential election.
"If we lose Mexico as a customer, it will be absolutely devastating to the ag economy," said Philip Gordon, 68, who grows corn, soybeans and wheat on a farm in Saline, Mich., that has been in his family for 140 years.
Gordon said he planned to call Trump at the White House "and remind him we need trade."
A Trump administration document that circulated on Capitol Hill last week appeared to present a more moderate approach to NAFTA negotiations, seeking to preserve much of the existing agreement and recognizing the interconnectedness of the two nations' economies, cultures and histories. Still, people involved in agricultural trade on both sides of the border said they were not about to rest easy on the basis of the document, which even the White House seemed to disavow.
"It's really hard to track with this president," said Todd Hultman, a grains analyst at DTN, an agriculture news and data service based in Omaha, Neb.
Mr. Trump has repeatedly asserted that Mexico has been the big winner under NAFTA, and the United States the loser. But many leaders in the U.S. agricultural and food industries hope Trump does not disrupt the agreement too much.
Many leaders in the U.S. agriculture industry say NAFTA has been a boon for farmers in the United States, particularly because it opened up new foreign markets and helped expand agricultural exports more than fourfold since the agreement was signed.
In 2016, the United States exported nearly $18 billion of agricultural products to Mexico, the third-largest market for these U.S. exports, according to the Department of Agriculture.
Mexico imported about 13.8 million tons of American corn last year, its government says. The Mexican government has not delayed in exploring other markets in which to purchase corn. A top agricultural official from Argentina visited Mexico City last month to discuss the possibility of increasing sales of Argentine yellow corn to Mexico. Officials from Mexico's Agriculture Ministry are planning a trip to Argentina and Brazil this month to discuss increasing corn purchases from those countries.
Last month, Mexico's deputy economy minister told the Financial Times that Mexico was exploring the possibility of allowing duty-free access to Argentine and Brazilian corn imports.
The showdown on NAFTA has also inspired Mexican agricultural officials and producers to step up programs that would increase domestic corn production and revive a sector undercut by the agreement, said Alejandro Vázquez Salido, director of Aserca, a Mexican government agency that supports farmers and promotes the marketing of Mexican agricultural products.
Some economists blame NAFTA for causing widespread unemployment in the Mexican agricultural sector by opening the floodgates to heavily subsidized American agricultural products, especially corn. A 2014 study estimated that 1.9 million agricultural jobs were wiped out, mainly those of small family farmers, helping to drive more illegal immigration into the U.S.