Final answer:
Senator Charles Sumner insulted Senator Andrew Butler of South Carolina in his speech, which led to Preston Brooks, Butler's cousin, assaulting Sumner with a cane in the Senate chamber.
Step-by-step explanation:
Senator Charles Sumner was insulting toward Senator Andrew Butler of South Carolina. During his impassioned "Crime Against Kansas" speech, Sumner made a controversial reference to Butler, accusing him of defending and desiring the institution of slavery. This outraged many Southerners, including Butler's cousin, Preston Brooks, who viewed Sumner's remarks as a personal affront to Butler and to Southern honor.
As Sumner was working at his desk on May 22, 1856, Brooks approached him, announcing his intention to punish him for the perceived libel against his state and relative. The altercation culminated in Brooks viciously assaulting Sumner with a cane, leaving him bleeding and unconscious.