A temporary Mexico-U.S. border crossing at San Ysidro shows President Donald Trump is serious about his threat to close the border in response to elevated levels of migration. The link between Tijuana and San Diego carried $33.79 billion of shipments as part of U.S. supply chains in the 12 months to Sept. 30. Should the border closure be repeated, or extended, U.S. importers may need to find alternative routes or use rail / air modes instead. Leading exporters using the northbound Tijuana truck route in the past 12 months include Samsung Electronics, Toyota Motor and Sony.