In a confrontational scene, an avuncular Taylor meets the concerned young Senator. Smooth-tongued and glib, Taylor tells Senator Smith about his "interest" in Willet Creek Dam and his persuasive boss-influence over all social institutions. He cooly attempts to buy Smith off by assuring him riches, political power and success if he remains silent about the Willet Creek Dam fraud. To his complete surprise, Jeff learns that his hero/idol Joseph Paine has expediently been in office for twenty years due to corruption:

Taylor: Anything that benefits the state is mighty important to me. Owning a lot of its industry, newspapers, and other odds-and-ends. Now if I felt that you had the welfare of the state at heart like I have, I'd say you were a man to watch. Now what do you like? Business? If you like business, you can pick any job in the state and go right to the top. Or politics? Huh? If you like being a Senator, there's no reason why you can't come back to that Senate and stay there as long as you want to. (Smith rises slowly and confronts Taylor eye-to-eye.) If you're smart. Now you take the boys here, or Joe Paine. They're doing all right. They don't have to worry about being re-elected or anything else. They're smart. They take my advice.
Smith: (in an incredulous tone) You mean you tell these men and Senator Paine what to do?
Taylor: Why yes. Joe Paine has been taking my advice for the past twenty years.
Smith: You're a liar.

In Senator Paine's office, decorated wall-to-wall with pictures, mementos, memorabilia and law books, Paine explains the reality of the situation, tells Jeff where he stands in relation to Taylor, and advises him to be less of an idealist:

I was hoping you'd be spared all this. I was hoping that you'd see the sights, absorb a lot of history, and go back to your boys. Now you've been living in a boy's world, Jeff, and for heaven's sakes, stay there! This is a man's world. It's a brutal world Jeff, and you've no place in it. You'll only get hurt. Now take my advice. Forget Taylor and what he said. Forget you ever heard of the Willet Creek Dam...I know it's tough to run head-on into facts but, well as I said, this is a man's world Jeff, and you've got to check your ideals outside the door, like you do your rubbers. Thirty years ago I had your ideals. I was you. I had to make the same decision you were asked to make today. And I made it. I compromised - yes! So that all those years, I could sit in that Senate and serve the people in a thousand honest ways. You've got to face facts, Jeff. I've served our state well, haven't I? We have the lowest unemployment and the highest federal grants. But, well, I've had to compromise. I've had to play ball. You can't count on people voting. Half the time they don't vote anyway. That's how states and empires have been built since time began. Don't you understand? (Pause) Well Jeff, you can take my word for it. That's how things are. Now I've told you all this because, well I've grown very fond of you. About like a son, in fact. And I don't want to see you get hurt.

Invoking their friendship and the friendship Paine had with Smith's father, Senator Paine begs Jeff to avoid interfering with the Deficiency Bill on the Senate floor: "You stay away from it. Don't say a word. Great powers are behind it and they'll destroy you before you even get started." Smith leaves Paine's office without a response, apparently left with no choice. He is unwilling to compromise and sacrifice his principles for a scheme involving graft, and he is feeling betrayed and let down by his sponsoring guide in the Senate. Moreover, he is overwhelmed by the realization that there is corruption in the men who were responsible for his appointment.

The next day, Smith fidgets during the reading of the Deficiency Bill and rises to question Section 40 regarding Willet Creek Dam. When it appears that Paine's corruption will be exposed, he interrupts Smith's words in mid-sentence and shifts blame toward Smith to frame him. The new tactic of the conspirators is to shift blame to Smith, and to discredit and accuse him of their own crime. The phony land purchases are shifted to him (with falsified documents and evidence) to show that the boys camp bill is Smith's own pork barrel - introduced for his own profit:

Mr. President. I have risen to a difficult task to say that out of evidence that has come to my attention, I consider Senator Smith unworthy to address this body...Senators, I have conclusive evidence to prove that my colleague owns the very land described in his bill. He bought it the day following his appointment to the Senate. And he's holding it, using this body and his privileged office for his own personal profit! Accordingly, I offer a resolution for an immediate inquiry by the Committee of Privileges and Elections as to the fitness of my colleague to continue to sit in this chamber.

Forcing Smith to be investigated by the Senate and branded for expulsion, Paine diverts attention from his own fraudulent actions. Smith is hissed and booed by the chamber - en masse, the young pages remove their Boy Ranger pins and throw them away.

In the committee hearings, trumped-up charges, false witnesses (Gov. Hopper and Sen. Paine testify falsely) and forged documents (a signed contract or deed to the land) are produced as evidence to show that Smith will enrich himself with the boys camp with "carefully laid plans to make an enormous profit out of the nickels and dimes scrapped together by the boys of this country." Smith stands silently for a moment looking at the seated Paine, who has his head bowed and refuses to acknowledge his presence face-to-face. Smith abruptly leaves the hearings, unable to prove his innocence.

Disillusioned, distraught, and disbelieving, Jefferson Smith makes a late-night visit (with his suitcases) to the Lincoln Memorial - his second (and presumably last) visit before leaving Washington. He notices the last sentence of Lincoln's 1863 Gettysburg Address inscribed on the marble wall: "AND THAT GOVERNMENT OF THE PEOPLE BY THE PEOPLE FOR THE PEOPLE SHALL NOT PERISH FROM THE EARTH." Now a broken man, he sits down on his bags which are packed in readiness to leave and begins to weep. From the darkened shadows, Saunders emerges and tells him: "You know, I had a hunch I'd find you here." She is thankful for having received a jar of strawberry preserves from his mother. From the newspapers, she tells him what she learned: "You certainly got to be a Senator."

Smith acknowledges her wisdom and cynical, Washington-wise savvy:

You sure had the right idea about me, Saunders. You told me to go back home, keep fillin' those kids full of hooey. Yeah. Just a simple guy you said was still wet behind the ears. A lot of junk about American ideals. Yeah, that's certainly a lot of junk, all right...I don't know. This is a whole new world to me. What are you gonna believe in? And a man like Paine, Senator Joseph Paine gets up and swears that I've been robbin' kids of nickels and dimes - a man I've admired and worshipped all my life. I don't know. There are a lot of fancy words around this town. Some of them are carved in stone. Some of 'em, I guess the Taylors and Paines have put 'em up there so suckers like me can read 'em. Then when you find out what men actually do - Well, I'm gettin' out of this town so fast and away from all the words and the monuments and the whole rotten show.

Crushed and downtrodden, Smith is determined to leave town, defeated and finished. In the somber, dim light of the Memorial, Saunders comes to realize that he sincerely loves the democratic process. Revitalizing him with her own rebirth of idealism and reminding him of the "faith" of the Founding Fathers (who were "fools" but the "odds against 'em didn't stop those men"), she encourages him to stand fast, stay and fight the machine-controlled Senate and the corrupt dam scheme of the scoundrels Senator Paine and Taylor:

Saunders: I see. When you get home, what are you gonna tell those kids?
Smith: I'll tell 'em the truth. Might as well find it out now as later.
Saunders: I don't think they'll believe you, Jeff. You know, they're liable to look up at you with hurt faces and say, 'Jeff, what did you do? Quit? Didn't you do something about it?'
Smith: Well, what do you expect me to do? An honorary stooge like me against the Taylors and Paines and machines and lies...
Saunders: Your friend Mr. Lincoln had his Taylors and Paines. So did every other man whoever tried to lift his thought up off the ground. Odds against 'em didn't stop those men. They were fools that way. All the good that ever came into this world came from fools with faith like that. You know that Jeff. You can't quit now. Not you! They aren't all Taylors and Paines in Washington. Their kind just throw big shadows, that's all. You didn't just have faith in Paine or any other living man. You had faith in something bigger than that. You had plain, decent, every day, common rightness. And this country could use some of that. Yeah - so could the whole cock-eyed world. A lot of it. Remember the first day you got here? Remember what you said about Mr. Lincoln? You said he was sitting up there waiting for someone to come along. You were right! He was waiting for a man who could see his job and sail into it. That's what he was waiting for. A man who could tear into the Taylors and root 'em out into the open. I think he was waiting for you Jeff. He knows you can do it. So do I.
Smith: What? Do what, Saunders?
Saunders: You just make up your mind you're not gonna quit and I'll tell you what. I've been thinkin' about it all the way back here. It's a forty foot dive into a tub of water, but I think you can do it.
Smith: Clarissa, where can we get a drink?
Saunders (slapping his knee): Now you're talkin'! (As they leave, he waves back at the seated, imposing figure of Mr. Lincoln.)

The next morning, Smith appears at his Senate desk to the consternation of the others in the chamber. Saunders waves and clasps her hands for him from the gallery high above. She tells Diz: "Pray Diz, if you know how." The report from the committee hearings on Jefferson Smith's expulsion is read, recommending that the resolution be adopted to expel him. The President of the Senate chooses to recognize Senator Smith and he is allowed to speak, having "an equal claim on the attention of this chair." From the gallery, Saunders cries: "Let him speak!"

Jefferson Smith begins his climactic, one-man filibuster scene (considered one of the virtuoso scenes of 1930s films), in part to stall a vote that would oust him from the Senate:

...I've got a few things I want to say to this body. I tried to say them once before and I got stopped colder than a mackeral. Well, I'd like to get them said this time, sir. And as a matter of fact, I'm not gonna leave this body until I do get them said.

In one of the film's unforgettable moments, the tension on the Senate floor is magnified. In a full shot of the chamber, Smith stands at his desk in the last row of Senators. In the same shot, Senator Paine in the first row rises and interrupts Smith, and without turning to face him, asks if the junior Senator will yield the floor. Smith insolently refuses to yield to Senator Paine, knowing something about the rules of yielding (from instructions and coaching received from Saunders):

No sir, I'm afraid not. No sir. I yielded the floor once before, if you can remember, and I was practically never heard of again. No sir. And we might as well all get together on this yielding business right off the bat now. (Laughter) Now, I had some pretty good coaching last night, and I find that if I yield only for a question or a point of order or a personal privilege, that I can hold this floor almost until doomsday. In other words, I've got a piece to speak, and blow hot or cold, I'm gonna speak it.

When he yields to a question from the dignified Senator Paine, Smith is reminded of the guilty charges brought against his character. Condemned, Smith responds:

Mr. President. I stand guilty as framed! Because Section 40 is GRAFT! And I was ready to say so, I was ready to tell you that a certain man of my state, a Mr. James Taylor, wanted to put through this dam for his own profit. A man who controls a political machine! And controls everything else worth controlling in my state! Yes, and even a man powerful enough to control Congressmen, and I saw three of them in his room the day I went up to see him...And this same man, Mr. James Taylor, came down here and offered me a seat in this Senate for the next twenty years if I voted for a dam that he knew and I knew was a fraud. BUT if I dared to open my mouth against that dam, he promised to break me in two. All right, I got up here and I started to open my mouth and the long and powerful arm of Mr. James Taylor reached into this sacred chamber and grabbed me by the scruff of the neck...

With a point of order, Paine admits to being one of the Congressmen in the room with Mr. Taylor, and accuses Smith of deliberately trying to "plant damaging impressions" of his conduct. In the meeting with Taylor, they were there for the purpose of bringing evidence against Smith and asking him to resign to avoid "bringing disgrace upon a clean and honorable state." Paine, with a show of raw power, denounces his junior Senator and then leaves the floor:

Gentlemen, I have lost all patience with this brazen character. I apologize to this body for his appointment. I regret I ever knew him. I'm sick and tired of this contemptible young man and I refuse to stay here and listen to him any longer. I hope every member of this body feels as I do.

Few in the Senate support Smith's requests to listen:

I want a chance to talk to people who'll believe me. The people of my state. They know me. And they know Mr. Taylor. And when they hear my story, they'll rise up and they'll kick Mr. Taylor's machine to kingdom come. Now I want one week to go back there and bring you proof that I'm right. And in the meantime, I want this Senate's promise that I will not be expelled and that the Deficiency Bill will not be passed.

Many of the Senators think it is an "affrontery" for Smith to dare to disgracefully stand there and ask for a postponement of the passage of the Deficiency Bill: "Why, millions will be without food and shelter. Public works will be at a stand-still." Smith challenges his political adversaries:

The people of my state need permanent relief from crooked men riding their backs.

When the chamber clears of Senators, Smith promises to endlessly speak in a classic filibuster. Prepared, he removes a supply of food and drink from his coat:

And I'll tell you one thing, that wild horses aren't gonna drag me off this floor until those people have heard everything I've got to say, even if it takes all winter.

With hand gestures suggesting what to do, Saunders provides heroic support from the balcony. During the 23-hour filibuster, Smith tries to gain time with a "call to quorum" while the results of his own investigation into corruption can reach him. Diz phones in his own story angle:

This is the most titanic battle of modern times. A David without even a slingshot rises to do battle against the mighty Goliath Taylor machine, allegedly crooked inside and out.

With Boss Taylor in control of the media, newspapers, and radio, the truthful distribution of Smith's message is doomed to fail. Taylor confidently tells Senator Paine: "I'll blacken this punk so that he'll...You leave public opinion to me." Taylor is relentless in seeking total victory over Smith, knowing the consequences if they fail:

If he even starts to convince those Senators, you might as well blow your brains out, you know that, don't ya? This is the works, Joe! Either we're out of business or we're bigger than we ever were before. We can't miss a trick. We can't stop at anything until we've smashed this yokel and buried him so deep...

But Senator Paine doesn't have the "stomach" to do anything more. His guilt-stricken conscience slowly softens him.

Banner headlines in the newspapers blast Smith's "cowardly" filibuster:

SMITH DISGRACES STATE
Criminal in Vicious Attack on Beloved Senator Paine
SMITH STOPS RELIEF!
Blocks Deficiency Bill - Starves Country to Save Hide
JAILBIRD DEFIES NATION
'Let The Poor Starve,' He Shouts

Radio announcements, banners ("STOP SMITH") and billboards ("SEND SMITH TO JAIL WHERE HE BELONGS," "SMITH TALKS - THE PEOPLE STARVE," and "GET BEHIND SENATOR PAINE") are part of Taylor's conspiracy to silence support for Smith.

During an informal caucus of the Senators with The President of the Senate, one of the Senators expresses his admiration for Smith's sincerity:

I didn't like this boy from the beginning. But most of us feel that no man who wasn't sincere could stage a fight like this against these impossible odds.

From the Senate itself, H. V. Kaltenborn (Himself) announces the Senate proceedings to the CBS radio audience:

Half of official Washington is here to see democracy's finest show, the filibuster, the right to talk your head off, the American privilege of free speech in its most dramatic form. The least man in that chamber, once he gets and holds that floor by the rules, can hold it and talk as long as he can stand on his feet providing always, first, that he does not sit down, second, that he does not leave the chamber or stop talking. The galleries are packed. In the diplomatic gallery are the envoys of two dictator powers. They have come here to see what they can't see at home. DEMOCRACY IN ACTION.

Throughout the entire filibuster sequence, the action cross cuts from scenes in the Senate chamber, to radio announcers, to reactions at home, to the Boy Rangers' support for Smith, to Taylor's manipulation of the party machine by telephone that orders crushing obstacles to be thrown in Smith's direction.

After reading from the Declaration of Independence (partially to stall for time), Smith preaches to the Senate and offers home-spun insight on democratic ideals:

Now, you're not gonna have a country that can make these kind of rules work, if you haven't got men that have learned to tell human rights from a punch in the nose. (The Gallery applauds) It's a funny thing about men, you know. They all start life being boys. I wouldn't be a bit suprised if some of these Senators were boys once. And that's why it seemed like a pretty good idea for me to get boys out of crowded cities and stuffy basements for a couple of months out of the year. And build their bodies and minds for a man-sized job, because those boys are gonna be behind these desks some of these days. And it seemed like a pretty good idea, getting boys from all over the country, boys of all nationalities and ways of living. Getting them together. Let them find out what makes different people tick the way they do. Because 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 - a little lookin' out for the other fella, too...That's pretty important, all that. It's just the blood and bone and sinew of this democracy that some great men handed down to the human race, that's all. But of course, if you've got to build a dam where that boys camp ought to be, to get some graft to pay off some political army or something, well that's a different thing. Aw no! If you think I'm going back there and tell those boys in my state and say: 'Look. Now fellas. Forget about it. Forget all this stuff I've been tellin' you about this land you live in is a lot of hooey. This isn't your country. It belongs to a lot of James Taylors.' Aw no! Not me! And anybody here that thinks I'm gonna do that, they've got another thing comin'. (He whistles loudly with his fingers in his mouth, startling Senators who are dozing or reading other materials) That's all right. I just wanted to find out whether you still had faces. I'm sorry, gentlemen. I-I know I'm being disrespectful to this honorable body, I know that. I- A guy like me should never be allowed to get in here in the first place. I know that! And I hate to stand here and try your patience like this, but EITHER I'M DEAD RIGHT OR I'M CRAZY.

After seven and one-half hours into the filibuster, one of the Senators proposes a motion to call for a recess until the morning. In a three-way routine between the rostrum (the President), the gallery (Saunders), and the floor (Smith), the twinkle-eyed President slyly looks up at Smith's coach in the gallery. Saunders, who knows the political ropes of Washington, signals for the uncomprehending Smith to not accept the motion. She gestures and points down toward the President, suggesting: "Ask him." The tolerant, amused President hides a smile of tacit approval for her coaching, and then explains how Smith would lose control of the floor if he accepted the motion for recess.

At a moment of crisis, Senator Smith is cheered and buoyed up after receiving a note taken to him on the floor by a young page. The note is from Saunders in the gallery with the acknowledgement of a long-distance courtship in the postscript:

Jeff
You're wonderful. Press boys all with you - Read them Constitution next very slow.
Diz says I'm in love with you.
P.S.
(He moves his thumb away to uncover the final few words)
He's right.

Smith faces media manipulation, false claims, and a "muzzling" of freedom of the press by the Taylor machine: "Not one word of what he's saying is being printed in that state. Taylor has practically every paper in the state lined up and he's feeding them doctored-up junk." Saunders transmits a dictation to Smith's mother (Beulah Bondi) that will be printed in the only free press left - Jeff's Boys Stuff publication. With the support of an army of faithful boys, the boys' paper is type-set with the headline: "JEFF TELLS TRUTH" - the only uncensored news available to Smith's constituents. With wagons and bicycles, the handbills are distributed in support of Smith, and the boys organize a parade. When the word that there is opposition reaches Taylor's headquarters, McGann sends the word out to confiscate and destroy the Boys Stuff newspaper and disrupt the parade, resulting in injuries to many of the boys. A carload of boys distributing newspapers is deliberately forced off the road by Taylor's forces, resulting in a gruesome crash and accident. Mrs. Smith phones Saunders, distressed by the repercussions: "Children hurt all over the city. Tell Jeff to stop!"

After twenty-three hours (and 16 minutes), with an agonizingly-weakened voice after many hours of filibustering, radio announcer Kaltenborn summarizes the fight on "the greatest floor in the land":

...It is the most unusual and spectacular thing in the Senate annals. One lone and simple American holding the greatest floor in the land. What he lacked in experience, he's made up in fight. But those tired Boy Ranger legs are buckling, bleary-eyed, voice gone, he can't go on much longer. And all official Washington is here to be in on the kill.

With an indomitable spirit but with a pleading, weary, pathetically hoarse voice, Smith has a few more exhortations for the Senators who have returned to watch the end of the filibuster. In an extraordinary metaphor emphasizing the Capitol Dome high above him, Smith imaginatively suggests re-positioning the lady of the Dome back to an ethical center where she belongs:

Just get up off the ground. That's all I ask. Get up there with that lady, that's up on top of this Capitol Dome. That lady that stands for Liberty. Take a look at this country through her eyes if you really want to see somethin'. And you won't just see scenery. You'll see the whole parade of what man's carved out for himself after centuries of fighting. And fighting for something better than just jungle law. Fighting so as he can stand on his own two feet free and decent, like he was created no matter what his race, color, or creed. That's what you'd see. There's no place out there for graft or greed or lies! Or compromise with human liberties! And if that's what the grown-ups have done with this world that was given to them, then we'd better get those boys camps started fast and see what the kids can do. And it's not too late. Because this country is bigger than the Taylors or you or me or anything else. Great principles don't get lost once they come to light. They're right here. You just have to see them again.

One final blow has been manufactured to defeat Smith - hundreds of "Taylor-made" phony telegrams from constituents in his state. Senator Paine is granted permission to bring in "evidence of the response" from his state. Baskets, wire barrels and bundles of stacks of 50,000 wired telegrams from constituents are deposited in the front of the Senate chamber. Paine holds up a fistful, telling Smith that they all demand that he yield the floor and give up his filibuster: "The people's answer to Jefferson Smith."

In one of the most powerful scenes ever filmed, Jefferson staggers forward in disbelief to look at the telegrams, pawing through them and desperately looking for some evidence of support. In a symbolic crucifixion stance, he grabs two large fistfuls and holds them out. With his hoarse voice, he turns toward Senator Paine and delivers an impassioned speech about "lost causes" - accusing Paine face-to-face of betraying his ideals:

I guess this is just another lost cause, Mr. Paine. All you people don't know about lost causes. Mr. Paine does. He said once they were the only causes worth fighting for. And he fought for them once, for the only reason that any man ever fights for them. Because of just one plain simple rule: 'Love thy neighbor.' And in this world today, full of hatred, a man who knows that one rule has a great trust. You know that rule, Mr. Paine. And I loved you for it, just as my father did. And you know that you fight for the lost causes harder than for any others. Yes, you even die for them. Like a man we both knew, Mr. Paine.

Then with heart-stirring courage, the bone-tired Smith finishes his heroic speech with a croaking voice:

You think I'm licked. You all think I'm licked. Well, I'm not licked, and I'm gonna stay right here and fight for this lost cause even if this room gets filled with lies like these, and the Taylors and all their armies come marching into this place. Somebody'll listen to me. Some...

Smith staggers, faints and collapses on the floor, dumping a basket of telegrams over onto himself. Sympathetically, Saunders screams from the gallery. With a strained look on his face, Senator Paine rushes from the Senate floor toward the vestibule/cloakroom as the stricken Smith is treated. Two or three shots ring out, and Paine is seen struggling with other Senators. They prevent him from killing himself, as he screams in a public confession:

I'm not fit to be a Senator. I'm not fit to live. Expel me! Expel me! Not him.

Conscience-stricken and in a fit of remorse at the last minute, Senator Paine saves the day. He re-enters the Senate floor and admits that everything Smith said was true - exonerating and vindicating him and the American political system:

Every word that boy said is the truth! Every word about Taylor and me and graft and the rotten political corruption of our 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!

The Senate and gallery erupt into wild cheering and applause at the miraculous victory of freedom and democracy over corruption. The figure of Smith is carried unconscious from the floor of the Senate. Young page boys are thrilled. Instrumental in his defeat of insurmountable odds, Saunders dances up and down with Diz in the gallery and then shouts "Yippee!" The President of the Senate sits back and watches the turmoil and jubilation, unable to restore order. Faith and vindication of Smith's idealism win out.