The seventh round of NAFTA negotiations from February 25 appear set to begin with the difficult issues of automotive rules of origin and agricultural market access. Mexico will want to leverage its position as a buyer of $12.1 billion of American basic foodstuffs in 2017, or 75% of its total of those products. The largest areas of exposure for U.S. farmers include corn ($2.7 billion of sales, where Brazil is already competing), soybeans ($1.6 billion, both Brazil and Paraguay can compete) and pork ($1.3 billion). The bigger controversy is access to Canada’s dairy sector. While America...