Three years before the release of “Mr. Smith Goes to Washington,” Frank Capra won his second Academy Award for Best Director for “Mr. Deeds Goes to Town.” Thematically, it bears a striking resemblance to “Mr. Smith,” as it’s about a good-natured fellow who gets brought into a new world to be taken advantage of by elites. In “Mr. Deeds,” the world is New York’s upper crust when the titular Deeds inherits the estate of his late uncle, worth about $20 million. He becomes the pawn for the greedy fat cats around to maneuver in order to get that money. It even costars Jean Arthur as a woman looking to take advantage of this yokel but who eventually falls for his folksy charm.
That film starred Gary Cooper, who was nominated for an Oscar for his performance. When Capra hopped aboard “Mr. Smith,” he envisioned it as a sequel to “Mr. Deeds,” hence the similar title. Whether it was meant as a direct or spiritual sequel is fuzzy, but Cooper was to be the lead. After some thought, Capra felt Cooper was a little long in the tooth for the role. Recounted in the book “James Stewart: Behind the Scenes of a Wonderful Life” by Lawrence J. Quirk, Capra said of Cooper playing Jefferson Smith:
“This boy had to get across that his strength was as the strength of 10 because his heart was pure, or a sure and solid variation on that beloved old cliché, but Cooper at that point was too experienced and sophisticated, for all his honesty and directness, to get across.”
So Capra turned to James Stewart, who he had just worked with on “You Can’t Take It with You,” and solidified Stewart’s movie star status.
Source : https://www.slashfilm.com/955891/james-stewart-wasnt-the-obvious-choice-for-mr-smith-goes-to-washington/