| Importance | Senator | Years |
| Famous for nullification debate with Sen. Robert Hayne | |
| Known as the 'Great Compromiser' and 'Judas of the West' | |
| Champion of states rights; started South Carolina's Nullifier Party | |
| Leader of the Compromise of 1850 and Kansas-Nebraska Act | |
| Was one impeachment vote away from becoming president | |
| Was famously attacked with a cane in the Senate chamber | |
| First and only former president to serve as a senator | |
| Leader of the Republican 'Stalwart' faction in the late 1800's | |
| First African American to serve as a US senator | |
| Leader of the Republican 'Half Breed' faction of the late 1800s | |