As of late Spring, 2018, negotiations between Mexico and the United States concerning changes to the North American Free Trade Agreement are reaching a climax. Mexican and U.S. negotiators have long agreed that, in order for any negotiated changes to have reasonable prospects of being made effective, the negotiations must conclude in May. The principal constraint thereafter lies in the combination of the months-long calendar for the U.S. Congress’s approval of the changes as stipulated by the 2015 act giving the President Trade Promotion Authority, and the termination of the current Congress in January 2019.