Jesús Seade, chief trade negotiator for incoming Mexican President Andrés Manuel López Obrador, has indicated the U.S.-Mexico-Canada Agreement (aka NAFTA) shouldn’t be signed sooner than November 30 unless U.S. section 232 duties on steel and aluminum are removed. President Trump may want an earlier, ceremonial, signing ahead of the U.S. midterm elections.

Mexican exports of steel and aluminum covered by the tariffs were worth $3.15 billion in the 12 months to August 31, or 6.6% of total U.S. imports of those metals. The potential winners on the U.S. side – assuming Mexico also...