Classic and beloved Capra-corn about an idealistic, nature-loving man from a small town who's given a fill-in senate position.
Jefferson Smith (James Stewart - one of my very favorite actors) adores Washington and Lincoln and the American Dream. He has a worshipful appreciation for democracy and political freedom.
When he arrives in Washington, he's mocked and teased by the jaded press and even more jaded senate staff. Little does he know or understand the political machinations that brought him to the Senate: he's meant to be a puppet and rubber-stamp a bill that will line the pocket of a certain political boss.
When the two sides clash, Smith nearly goes home in disgrace. It's the love and dedication of one of the jaded staffers he's won over that keeps him on the Senate floor in a climactic, exhausting filibuster.
The movie ends suddenly, leaving several loose ends, but since it's a Capra movie, we know that the good guys will have won and love conquers all.
I rank this in my top 100 movies, if only because I'd like everyone to feel so earnestly and work as doggedly for what they believe in. Idealism at its best.