It's been almost 20 years since Dan Rather signed off as anchor and managing editor of the "CBS Evening News," at the network where he spent 44 years covering wars, politics, and the assassination of JFK – and where he mentored a young correspondent named Lee Cowan. Rather, now 92, talks with Cowan about his illustrious career; about the story that gave him (and CBS) a black eye; and his post-CBS years, writing books and finding a new, younger audience on social media.