Farm groups expressed alarm Monday at President Donald Trump's renewed threats to shut down the southern border, which could cripple trade with Mexico, an irreplaceable market for billions of dollars of milk, ham, rice, potatoes and corn.

USDA data show the U.S. shipped about $19 billion worth of ag products to Mexico in 2018 and a loss that big would be catastrophic for a farm sector already reeling from depressed prices.

“We are at the breaking point and cannot afford a total loss of the Mexican market, one that accounted for more than 20 percent of total U.S. pork exports last year,” says David Herring, president of the National Pork Producers Council.

Trump, speaking to reporters Friday, railed against new “caravans” of migrants and the U.S. trade deficit with Mexico. He threatened to shut down the border completely and stressed, “It could be to all trade.”

Trump has threatened to shut down the border before, but concern this time around was heightened after White House Chief of Staff Mick Mulvaney took to Sunday talk shows to back up the president’s threat.

“We have, right now, two big caravans coming up from Guatemala,” Trump said. “Massive caravans walking right through Mexico.  So, Mexico is tough.  They can stop them, but they chose not to.”

Trump was very serious, Mulvaney said on ABC’s This Week and CNN’s State of the Union.

“Why are we talking about closing the border?” Mulvaney said on ABC. “Because not for spite and not to … undo what's happening but to simply say look, we need the people from the ports of entry to go out and patrol in the desert where we don't have any wall.”

But shutting down trade would be a deadly blow for U.S. dairy farmers, said Tom Vilsack, president and CEO of the U.S. Dairy Export Council.

"Dairy exporters already are suffering from diminished access to export markets due to high tariffs and lack of progress on U.S. trade agreements," Vilsack said. “Closing the U.S. southern border to Mexico would be a gut punch that could set the industry back by a decade or two."

The American dairy industry as well as American pork producers are already hurting because of Mexican retaliatory tariffs in a battle with the U.S. over steel and aluminum trade.

"A cloud of uncertainty and restricted access to our most important export markets have strained U.S. pork producers and their families for more than a year,” NPPC’s Herring said. “The value of our exports to Mexico and China are down 28 percent and 32 percent, respectively, this year.”

The U.S. Chamber of Commerce also warned about the consequences of disrupting U.S.-Mexico trade. “Closing the US-Mexico border would inflict severe economic harm on American families, workers, farmers and manufacturers across the United States.  … Even threatening to close the border to legitimate commerce and travel creates a degree of economic uncertainty that risks compromising the very gains in growth and productivity that policies of the Trump administration have helped achieve," the chamber said. 

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