In the early seventies I was the road manager for The Johnny Mann Singers. One year we got a gig at the Riviera Hotel in Vegas as the opening act for Don. Right after our performance I would stand in the wings and be amazed and impressed at the way he did his act. He looked like he was being spontaneous and ad-libbing, but in reality had a set of reactions and lines prepared for any and every circumstance from the audience. That showed me what it really means to a professional entertainer at the top of his game.