ARLINGTON, VA - SEPTEMBER 11: An American flag is draped over the Pentagon where it was hit by an airliner 15 years ago, September 11, 2016 in Arlington, Virginia. Later in the day President Obama will visit the Pentagon and speak on 15th anniversary of the September 11th terrorist attacks that killed nearly 3,000 people at the World Trade Center, Pentagon and on Flight 93. (Photo by Mark Wilson/Getty Images)