US Historians, what is the most outrageous thing to happen in a session of Congress?

Threatening a man with a pistol is one thing, but actually using deadly force against him would be more outrageous.

In 1856 shortly before the Civil War, Sen. Charles Sumner delivered a fiery abolitionist speech in the Senate that accused Sens. Stephen Douglas (D-IL) and Andrew Butler (D-SC) of being responsible for violence in Kansas and seriously questioned their character and fitness for their office. Among some residents of the antebellum-era American South, serious insults were grounds for duels or use of physical force to reclaim a perceived loss of honor.

But Sumner had insulted Butler deeply. Representative Preston Brooks (D-SC) was Butler's ally and took action on his behalf. Sen. Butler was not present during Sumner's speech. Brooks brought a metal-tipped cane into the Senate chamber after session had adjourned for the day. Sumner was still sitting there when Brooks slammed the cane into his head. He repeatedly struck Sumner, who tried to crawl away while Brooks beat him mercilessly.

Sumner suffered from head trauma, constant nightmares and severe headaches. He also suffered from what would now be diagnosed as post-traumatic stress disorder. Being that PTSD wasn't understood at the time, he was accused of cowardice and failure to perform his duties as senator. He eventually recovered and served in the Senate until 1874. He is best known for being a major advocate of emancipation, allowing blacks in the Union army, and giving freed slaves the right to vote.

That "honor" probably has to go to the beating of Senator Charles Sumner by Representative Preston Brooks.

Sumner was one of the senators for Massachusetts and an outspoken abolitionist and critic of slavery. In 1856 during the Bleeding Kansas crisis, he made a very long, vitriolic speech against the Kansas-Nebraska Act, called the "Crime Against Kansas" speech, where he called for the immediate entrance of Kansas into the Union as a free state, compared the attempts of Southern slaveholders to make Kansas a slave state to the rape of a virgin, and personally attacked the authors of the Kansas-Nebraska Act, Stephen Douglas (senator from Illinois), and Andrew Butler (senator from South Carolina), and followed that up by attacking South Carolina itself, leading to my favorite line.

Were the whole history of South Carolina blotted out of existence, from its very beginning down to the day of the last election of the senator to his present seat on this floor, civilization might lose -- I do not say how little, but surely less than it has already gained by the example of Kansas...

During the speech, Douglas is supposed to have remarked to a colleague, "This damn fool Sumner is going to get himself shot by some other damn fool." He came pretty close.

That brings us to Rep. Preston Brooks. Brooks was Senator Butler's nephew, and considered the attack a personal insult. He thought about challenging Sumner to a duel, and asked one of the other congressmen for South Carolina, Lawrence Keitt, for advice. Keitt's position was that dueling was for men of equal social standing, and Sumner was "no better than a drunkard." Brooks concluded that if that was the case, a public beating was in order to punish Sumner.

Two days after the speech, Brooks approached Sumner in the Senate chamber, accused him of libel, and began beating him with his cane, a thick, heavy thing with a gold head. Sumner tried to stand up, but Brooks knocked him over and trapped him under his desk, which was bolted to the floor. Brooks continued to assault Sumner until the senator tore the desk out of the floor and, blinded by his own blood at this point, attempted to flee up the aisle, but he collapsed into unconsciousness. Brooks chased him down and continued to beat Sumner after the senator collapsed, only stopping when his cane finally broke.

Why did nobody try to stop this? Because Lawrence Keitt had drawn a gun and was pointing it at the rest of the Senate, shouting to "let them be!"

Keitt was censured for his part in all this- he resigned in protest, and South Carolina overwhelmingly re-elected him to his old seat less than two months later. in 1858 he would be censured again, this time for attempting to strangle Pennsylvania Rep. Galusha Grow for calling him a "Negro driver", an event that eventually turned into a brawl involving more than 50 members of Congress.

Brooks received hundreds of canes from proslavery admirers to replace his broken one. He was arrested for assault and fined $300 (around $8,000 today, give or take) but served no jail time. He remarked that he never meant to kill Sumner- if he had, he would have used a different weapon. An attempt to expel him from the house failed, but he resigned anyway. A month later, a special election had him back in his seat in the House. He died less than a year later, of a respiratory infection.

Sumner very nearly died, and suffered severe head trauma, which caused him chronic pain for the rest of his life, as well as "Psychic wounds," what today we know as PTSD. It took him three years to recover enough to return to the Senate (his constituents reelected him in the meantime, leaving his chair in the Senate empty as a symbol), and he never truly recovered from the assault, like I said, suffering from the effects the rest of his life.

Edit: we all had the same idea, didn't we? It's a head or two above the rest for sure. :P