Security contributor: "We are facing the most complex threat environment" in U.S. history

Sam Vinograd, CBS News national security contributor, joined "Face the Nation with Margaret Brennan" with CBS News law enforcement analyst AT Smith after the White House Correspondents' Dinner shooting, saying that the U.S. is facing "the most complex threat environment in our nation's history, in particular, from lone actors, individuals who radicalized to violence, often online."