One of the many things I love about this movie is the avuncular way that the Harry Carey's President of the Senate treats Jeff on the day of his swearing in, and his barely restrained glee when Jeff was working up to the filibuster. His facial expressions and the way he kept bringing his hand up to try and hide his smile were really nice touches by Carey.
It has been about thirty years since I read Frank Capra's autobiography 'The Name Above The Title' and my memory may be a little sketchy but I think Capra's commentary went something like this. "We had a tricky job casting the Vice President (President of the Senate) and kept going through the US Film Actors Handbook. I suddenly saw Harry Carey's great American face looking back at me and knew he was our man. His big scene was the swearing-in of Smith. Carey's first run-throughs were awful. I had to take him on one side and have a word with him. I said 'Harry, you aren't a former silent move western actor, you are the Vice President of the United States. Now play the scene again. Well, Carey grew six inches taller and went through the scene perfectly. His sympathetic performance is one of the most fondly remembered in the whole movie, and earned Carey an Academy Award Nomination."
I'm sure Carey would have been a popular winner of the Best Supporting oscar. The winner that year was that stalwart scene stealer Thomas Mitchell, who co-starred in Mr Smith as the reported Diz Moore. Mitchell won for playing Doc Boone in John Ford's Stagecoach.