What was the impact of the Lincoln-Douglas debates?

The Lincoln-Douglas debates were born out of recriminations over political decisions such as the Dred Scott case and the Kansas-Nebraska Act. These examples—the former dealing with a landmark Supreme Court decision not to include blacks under the list of citizens granted protection by the Constitution and the latter having repealed the Missouri Compromise, granting individual territories the right to determine their own laws regarding slavery rather than prohibiting it in the northern states outright—were symptomatic of a larger public dispute concerning the immorality of human slavery.

The contrasting political philosophies of Abraham Lincoln and Stephen Douglas essentially represented the age-old dispute as to whether decisions of national significance should be left to individual states or should be absorbed in the purview of the federal government. Senator Douglas, a Democrat, represented the former view, Republican Abraham Lincoln, the latter.

Douglass specifically advocated for what he called “popular sovereignty,” which he believed to be the bulwark of democratic governance. For him, the ability for state governments and state legislatures to determine what was and was not in the best interest of the peoples under their jurisdiction, including questions of slavery, was the hallmark of local self-government—the principles upon which, he argued, the country had been founded.

Thus, Douglass supported the rationality of the Kansas-Nebraska Act, which gave state governments power to determine whether they would tolerate the institution. For example, when Lincoln pressed him as to how popular sovereignty could be reconciled with the fact that some slave-holders transported their slaves into free states, Douglass famously replied with his “Freeport Doctrine.” Whatever the government may say regarding the legality of slavery, it could never exist anywhere unless it were supported by local police institutions. This statement ominously foreshadowed the coming Civil War.

Abraham Lincoln was a fair-minded, equable child of the frontier. He had a keen mind for the way practical experience intersected with the larger principles of morality upon which the Constitution had been founded. He abhorred slavery on moral grounds but understood that it could not be eradicated overnight. To eliminate the institution by official decree would be disastrous for the Southern economy and would undoubtedly lead to social collapse.

Instead, Lincoln believed that slavery needed to die naturally, fading over time into an anachronistic obscurity. In his arguments with Douglass, Lincoln stressed that blacks had an equal right to the fruits of their own labor and emphasized Douglass’ indifference to the quotidian suffering of the enslaved person’s everyday existence.

These debates were important because they indicated what mentalities America’s major political figures held on the eve of the Civil War. In the early years of the conflict, from around 1861–62, Lincoln is said to have never predicated the ongoing efforts of the Union army on abolitionism—a decision, he argued, that would only further disintegrate the Union. Rather, as reflected in his debates with Douglas, he was first and foremost committed to maintaining the sanctity of the United States, keeping critical border states like West Virginia and Kentucky loyal to the North, and preventing an irreversible schism. It was only after the defeat of the Confederate Army was a foregone conclusion, and the stability of his norther alliances was guaranteed, that he issued his Emancipation Proclamation.

The only real impact of the debates between Abraham Lincoln and Stephen Douglas in 1858 was that they put Lincoln on the national "map" as a major political figure.

The debates were staged as part of a race between the two men for a seat in the US Senate.  Douglas won the election.  Even so, the debates catapulted Lincoln into the public eye.  They were widely covered by various newspapers because Douglas was such an important national figure.  Debating Douglas allowed Lincoln to become much better known and therefore contributed greatly to his becoming president two years later.

How did the Lincoln-Douglas Debates shape political debates over slavery?

Stephen Douglas was a challenging opponent for Abraham Lincoln when the two were running for election to the Senate for the state of Illinois in 1858.  Douglas chose the politically expedient route, advocating throughout the series of debates that popular sovereignty was the only way to settle the issue; let the people of a new territory decide, he said, whether or not slavery would be allowed.  Douglas took issue with Lincoln's declaration that "A house divided against itself cannot stand." While Lincoln insisted that the nation would not be able to function indefinitely as half-slave/half-free, Douglas argued that it (the United States) had always existed that way, and would continue in perpetuity if the people of a territory could simply be left to their own devices. 

Lincoln, for his part, acknowledged that he did not believe blacks equal to whites, but that he did believe the system of slavery was fundamentally at odds with the ideals of the United States Constitution in particular, and democracy in general.  In conjunction with this focus on the ideals of the nation, Lincoln did not hesitate to mention as a matter of course that Douglas's authorship of the Kansas-Nebraska Act had overturned the Missouri Compromise of 1820, and didn't it appear that perhaps Douglas's primary agenda was to keep the slaveowning coalition happy?

While Douglas may have won the battle, so to speak, Lincoln won the war.  Douglas was elected to the Senate in 1858; however, when next the two men met on the political field, in the presidential election of Lincoln had the clear advantage.  His remarks in the 1858 campaign had earned him a reputation as a reasonable moderate, and his focus on higher democratic ideals gave him a staying power that Douglas's short term solution simply could not offer.  In short, Lincoln seemed to have a vision for a great nation, while Douglas seemed to many to have had only a vision for getting elected.