Slow progress on ratification of the U.S.-Mexico-Canada Agreement (USMCA) raises the risk that a carve out for Mexico and Canada from America’s forthcoming section 232 tariffs on the automotive industry may not be applied. President Donald Trump has to make a decision on those duties by May 17. The delays come as Mexican exports of cars and light trucks fell 0.1% year over year in February, led by a drop in shipments by Fiat Chrysler and General Motors. Volkswagen by contrast, which has a lower exposure to the U.S. and hence any new tariffs, saw an increase in exports. The U.S. accounted...