The Dig: Trump's Wall Has Already Been Built

Donald Trump pledged to build a big, beautiful wall on the border with Mexico. For liberals, the wall now shares a toxic association with Trump. But until recently, militarizing the border with Mexico was accepted as a core piece of the commonsense, bipartisan establishment immigration and drug policy agenda. Dan talks about border policy with Peter Andreas, a professor at Brown University and the author of Border Games: Policing the US-Mexico Divide.