As the architect of the Kansas-Nebraska Act, Douglas was one of the most prominent politicians in the country and seen as a future presidential contender. The controversial 1854 law repealed the Missouri Compromise and established the doctrine of popular sovereignty, by which each new territory joining the Union would decide for itself whether to become a free or slave state.

Opposition to the Kansas-Nebraska Act had drawn Lincoln, a lawyer and former one-term Whig congressman, back into the political arena. He launched a Senate run in early 1855 but stepped aside to make way for another candidate.

By 1858, Lincoln was the most prominent leader in the new Republican Party in Illinois, and the clear choice to run against Douglas. He kicked off his campaign in earnest with a speech in Springfield that June, in which he famously declared that "A house divided against itself cannot stand..this government cannot endure, permanently half slave and half free.”

Lincoln and Douglas met in seven debates between August and October 1858, located in different congressional districts around the state. In all, they traveled over 4,000 miles during the Senate campaign. While Lincoln traveled by railroad, carriage or boat, Douglas rode in a private train fitted with a cannon that fired a shot every time he arrived in a new location.

Each debate followed the same structure: an hour-long opening statement by one candidate, an hour and a half-long response by the other candidate and a half-hour rebuttal by the first candidate. Despite their length and often tedious format, the debates became a huge spectacle, attracting crowds of up to 20,000 people. Thanks to the many reporters and stenographers who attended, and new technologies such as the telegraph and the railroad, the candidates’ arguments drew national attention, and would fundamentally alter the national debate over slavery and the rights of Black Americans.

Aside from the physical contrast—Lincoln was tall, lanky and rumpled; Douglas short, stocky and dressed in expensive suits—the two men represented starkly opposing viewpoints on the issues at hand. From their first debate on August 21 in Ottawa, Douglas accused Lincoln of running on a radically antislavery “Black Republican” platform and attempted to link him with leading abolitionists like Frederick Douglass.

Lincoln attacked Douglas for his support of the Supreme Court’s notorious 1857 decision in the Dred Scott case, which denied citizenship to all Black people, enslaved or free, and accused him of seeking to make slavery legal throughout the United States. In the second debate, on August 27 in Freeport, Lincoln asked Douglas whether or not popular sovereignty allowed settlers to exclude slavery from a territory before it joined the Union. Douglas said yes, clarifying that territories could choose not to enforce Dred Scott by withholding protection for slaveholders under local law. Known as the Freeport Doctrine, this stance alienated many Southerners and would come back to haunt Douglas during his 1860 presidential run.

Douglas backed the idea (common to Jacksonian Democrats) that power was best exercised at the local level. By contrast, Lincoln argued that only the federal government had the power to abolish slavery.

Douglas repeatedly attacked Lincoln’s supposed radical views on race, claiming his opponent would not only grant citizenship rights to freed slaves but allow Black men to marry white women (an idea that horrified many white Americans) and that his views would put the nation on an inevitable path to war. Lincoln responded that he had “no purpose to introduce political and social equality between the white and the Black races” and that “a physical difference between the two” would likely prevent them from ever living in “perfect equality.” Though he believed slavery was morally wrong, Lincoln made it clear that he shared the belief in white supremacy held by Douglas and nearly all-white Americans at the time.

But while Douglas held that the nation’s founding document had been written by white men, who intended it to apply only to white men, Lincoln argued that “there is no reason in the world why the negro is not entitled to all the natural rights enumerated in the Declaration of Independence.” Though he assured Southerners he did not plan to interfere with slavery where it already existed, he argued that the Founding Fathers—many of whom enslaved people—had regarded the institution of slavery as a moral evil that must eventually disappear.

In the elections held in November 1858, Lincoln and other Republican candidates won 53 percent of the popular vote statewide. But the congressional districts represented in the Illinois legislature at the time favored the Democrats, and the state legislature chose to return Douglas to the Senate.

Despite his loss, Lincoln’s commanding performance in the debates with Douglas, and his eloquent and bold statement of the Republican Party’s position on slavery, established him as a figure of national importance. Over the next two years, he would hone his arguments on the morality of slavery in speeches around the country, emerging as the dark horse Republican nominee in the 1860 presidential election.

Meanwhile, Douglas’ Democratic Party continued to split over the issue of slavery’s extension. Douglas succeeded in winning the Democratic nomination in 1860, but with Southern Democrats backing John Breckenridge, he won only one state: Missouri. Exhausted by the campaign, as well as his efforts to rally northern Democrats to the Union cause as the Civil War began, Douglas died in June 1861, at the age of 48.

Fergus M. Bordewich, “How Lincoln Bested Douglas in Their Famous Debates.” Smithsonian, September 2008.

Eric Foner, The Fiery Trial: Abraham Lincoln and American Slavery (W.W. Norton, 2010)

Doris Kearns Goodwin, Team of Rivals: The Political Genius of Abraham Lincoln (Simon & Schuster, 2005)