President Obama will address the nation Monday night about U.S. involvement in Libya in a speech that will likely be one of the most important on foreign policy so far. It is a chance for the president to explain why we’re in Libya and to demonstrate that he has a plan for U.S. involvement in the conflict. Bruce Jentleson, Professor of Public Policy and Political Science at Duke University, and former State Department senior adviser says that this will be a defining moment for Obama’s presidency.