When Shep is talking to Charlie in the garage, he shows him a picture of his son after getting out of Sierra Tucson Rehab Center. This is the same fictional rehab center used in a story arc/plot line on The West Wing (1999). Both series were written and created by Aaron Sorkin.
Jane Fonda (Leona Lansing) & Sam Waterston (Charlie Skinner) also worked together on Grace and Frankie (2015) as Grace Hanson & Sol Bergstein respectively.