In the 1970s, one-man Broadway shows were quite common. For example, there were shows with actors playing the likes of Mark Twain, Will Rogers and Groucho Marx. So, it's not surprising that Henry Fonda would do his own one-man show about the famous lawyer, Clarence Darrow.
I was amazed as the show apparently was NOT a success and only went for 29 performances. Apparently, however, someone liked the play and convinced the powers that be to record it and play it on television...and once again with Fonda in the lead....who also happened to look quite a bit like Darrow.
As for the play, it consists of a simple set and Fonda pretending to be Darrow. He then talks about his life, various important court cases he handled and his life philosophy. As for this, some viewers might be put off with Darrow's seemingly atheist (or at least agnostic) beliefs, though in many ways these views and Darrow's politics are quite in line with Fonda's. This might also account for the comment about Republicans and Democrats and slavery, as noted in the IMDB trivia, as it seemed more a jab by Fonda about CURRENT Republicans than an accurate comment about slavery (which was strongly associated with the pro-slavery Democrats at the time).
Overall, an amazing one-man performance...worth seeing even if you are not the biggest fan of Fonda or Darrow.