What role do Mexico, Canada and China play in the flow of fentanyl into the United States?

President Donald Trump’s plan to impose tariffs on goods from Mexico, Canada and China is partly aimed at curbing the flow of fentanyl into the United States, where the opioid is blamed for some 70,000 deaths annually. So how do those countries play a role in the trafficking of the drug?  Plus, we take a closer look at how global car companies are particularly vulnerable to tariffs. Editors’ note: Since this update, the US has also agreed to pause tariffs on Canadian imports.