President Donald Trump, Canadian Prime Minister Justin Trudeau and Mexican President Enrique Peña Nieto signed the new U.S.-Mexico-Canada Agreement — or USMCA — in Buenos Aires last week.

“The new USMCA makes important specific changes that are beneficial to our agricultural producers” said U.S. Agriculture Secretary Sonny Perdue. “We have secured greater access to the Mexican and Canadian markets and lowered barriers for...