It was past time for him to do so leaving the politics out of it he has not looked or sounded good for the past several years and the fact the network had relegated him to MSNBC says a lot about how they saw him.
An amazing 55 year network news career. Not surprising he is not looking well, as he was diagnosed with an incurable blood cancer in 2013 (multiple myeloma). Scored major coups such as being the first english speaking journalist to report on the fall of the Berlin Wall from Berlin, attending a conference in East Berlin at the time. He was there when the East German Politburo spokesman made the announcement and then reported on it from the Brandenberg Gate. He has interviewed presidents, foreign leaders of both the free world and Communist countries, received the Presidential Medal of Freedom, French Legion of Merit, at least 7 Emmy Awards, Edward R Murrow Award, Sylvanus Thayer Award from The United States Military Academy at West Point and a laundry list of other awards and honorary degrees from prestigious universities and organizations civilian and military across the country.
Pretty amazing life. He did good. I wish him well.