In the months leading up to the attack on the U.S. Capitol on 6 January 2021, there were reported efforts to organize large groups of protestors to travel to Washington, D.C. to dispute the outcome of the 2020 presidential election. Over the course of about 7 hours on 6 January, the attack on the U.S. Capitol resulted in assaults on approximately 140 police officers. In addition, the events of the day led to at least seven deaths. Questions have been raised about the extent to which necessary steps were taken to adequately secure the Capitol Complex and share intelligence information. The Federal Government was unprepared for this insurrection, even though it was planned in plain sight on social media for the world to see. And despite all the military and law enforcement resources our Government can call upon in a crisis, security collapsed in the face of the mob, and reinforcements were delayed for hours as the Capitol was overrun. This book tries to understand what went wrong that day to prevent this from ever happening again.