Homeland Security Secretary Kirstjen Nielsen has defended the Trump administration’s controversial "zero tolerance" immigration policy that has led to families being separated at America’s southwest border. In this discussion, she addresses illegal immigration, saying it reflects a broken system. Her conversation with Peter Alexander, national correspondent for NBC News, also touches on Russian meddling in the 2016 presidential campaign and terrorism. Alexander asks if homegrown, lone-wolf terrorism is the greatest threat today in the US. Their conversation on June 19 was part on the Aspen Security Forum held by the Aspen Institute’s Homeland Security Program.