Factual error: The filibuster scene gives the impression that the Senators were powerless to stop Jefferson Smith's speech. However, they can make a speaker shut up if at least 3/5 of the Senators vote to. From the Senators' reactions, a lot of them probably would have voted to silence Smith. (Clearly, if this had happened, the movie would be much less interesting).
Jefferson Smith: I wouldn't give you two cents for all your fancy rules if, behind them, they didn't have a little bit of plain, ordinary, everyday kindness and a little looking out for the other fella, too.
Jefferson Smith: I can promise you one thing, I'll do nothing to disgrace the office of - the United States Senate.
Senator Joseph Paine: Let me go! I'm not fit to be a senator! I'm not fit to live! Expel me, not him! Willet Dam is a fraud! It's a crime against the people who sent me here - and I committed it! Every word that boy said is the truth! Every word about Taylor and me and graft and the rotten political corruption of my state! Every word of it is true! I'm not fit for office! I'm not fit for any place of honor or trust! Expel me, not that boy.