What did stephen douglas do that has him immortalized in history

He was one of two Democratic Party nominees for president in the 1860 presidential election, which was won by Republican Abraham Lincoln. American politician, leader of the Democratic Party, and orator who espoused the cause of popular sovereignty in relation to the issue of slavery in the territories before the American Civil War (1861–65). He was reelected senator from Illinois in 1858 after a series of eloquent debates with the Republican candidate, Abraham Lincoln, who defeated him in the presidential race two years later.