It's been nearly 20 years since the terrorist attacks of September 11, 2001. The Chertoff Group's Jayson Ahern, Charles Allen, Adam Isles, General Michael Hayden, and Lee Kair reflect on a day that changed America, and share stories about how it influenced their careers. They had a front-row seat to what happened on one of the country's darkest days — and witnessed a nation that rose to the challenge.