On the 15th anniversary of the September 11 terror attacks on US soil, Thomas Sanderson, Senior Fellow and Director of the Transnational Threats Project at the Center for Strategic and International Studies (CSIS) and Nadia Oweidat, Middle East Fellow at New America, discuss with host Carol Castiel progress made and challenges ahead in the fight against violent extremism, whether from al Qaida affiliated groups, the so-called Islamic state, lone wolves and state sponsors of terror.