One year ago this month, Joe Biden’s performance at the first U.S. presidential debate against Donald Trump sparked global headlines – and rang alarms – about his mental and physical acuity, culminating in Biden's eventual withdrawal from the race. After the Democrats went on to lose the election, CNN anchor Jake Tapper and Axios political reporter Alex Thompson began investigating the roots of Biden's decline. In their new book Original Sin, they argue that his inner circle went to great lengths to cover it up. Tapper joins Piya Chattopadhyay to make his case, and respond to the criticism his reporting has received from across the political spectrum.