Gordon Hanson (University of California San Diego) joins Keynes and Bown to explain the migration and humanitarian crisis at the heart of President Trump’s threat to impose new tariffs on imports from Mexico. They discuss the history of undocumented migration arising since the 1960s, as well as how it has been impacted by changes in US and Mexican economic conditions and immigration policies. They also describe how the crisis has been affected by rising violence in Guatemala, El Salvador, Honduras and Mexico, as well as the unintended consequences of US and Mexican migration and asylum policies.