For Lincoln, they were an opportunity to raise both his state and national profile and that of the burgeoning Republican Party, newly organized four years before in Ripon, Wisconsin, in 1854.

The debates focused on slavery, specifically whether it would be allowed in the new states to be formed from the new American western federal territories acquired through the earlier Louisiana Purchase of 1803, and the more recent Mexican Cession of 1849.

[2] Douglas, as the Democratic candidate, held that the decision should be made by the residents of the new states themselves rather than by the federal government (popular sovereignty).

[4] New technology had become available in recent years: railroad networks, the electric telegraph with its Morse code, and Pitman shorthand writing, at that time called "phonography".

They raced to meet the next train to Chicago, handing the notes to railway riding stenographers who during the journey converted the shorthand symbols and abbreviations back into their original words, producing a transcript ready for the Chicago typesetters printing presses, and for the telegrapher, who sent the texts to the rest of the country east of the Rocky Mountains, which was as far as the telegraph wires reached.

Some newspapers helped their preferred candidate with minor corrections, reports on the audience's positive reaction, or tendentious headlines ("New and Powerful Argument by Mr. Lincoln–Douglas Tells the Same Old Story").

Newspapers reported 12,000 in attendance in Ottawa (Illinois),[8] 16,000 to 18,000 in Galesburg,[5] 15,000 in Freeport,[9] 12,000 in Quincy, and at the last debate in Alton, 5,000 to 10,000.

[7] The debates near Illinois's borders (Freeport, Quincy, and Alton) drew large numbers of people from neighboring states.

[citation needed] The Gilder Lehrman Institute of American History's Mr. Lincoln and Friends Society notes that prominent Bloomington, Illinois resident Jesse W. Fell, a local real estate developer who founded the Bloomington Pantagraph and who befriended Lincoln in 1834, had suggested the debates in 1854.

During his tenure in the Congress, he disagreed with Douglas and supported the Wilmot Proviso, which sought to ban slavery in any new territory.

[15] Before the debates, Lincoln charged that Douglas was encouraging fears of amalgamation of the races, with enough success to drive thousands of people away from the Republican Party.

[16] Douglas replied that Lincoln was an abolitionist for saying that the American Declaration of Independence applied to blacks as well as whites.

[17] Lincoln argued in his House Divided Speech that Douglas was part of a conspiracy to nationalize slavery.

He expressed the fear that any similar Supreme Court decision would turn Illinois into a slave state.

I hate it because it deprives our republican example of its just influence in the world—enables the enemies of free institutions, with plausibility, to taunt us as hypocrites—causes the real friends of freedom to doubt our sincerity, and especially because it forces so many really good men amongst ourselves into an open war with the very fundamental principles of civil liberty—criticizing the Declaration of Independence, and insisting that there is no right principle of action but self-interest.Lincoln said in the first debate, in Ottawa, that popular sovereignty would nationalize and perpetuate slavery.

[23][24] The Compromise of 1850 allowed the territories of Utah and New Mexico to decide for or against slavery, but it also allowed the admission of California as a free state, reduced the size of the slave state of Texas by adjusting the boundary, and ended the slave trade (but not slavery itself) in the District of Columbia.

[26] There were partisan remarks, such as Douglas's accusations that members of the "Black Republican" party were abolitionists, including Lincoln, and he cited as proof Lincoln's House Divided Speech, in which he said, "I believe this government cannot endure permanently half slave and half free.

"[27] Douglas also charged Lincoln with opposing the Dred Scott decision because "it deprives the negro of the rights and privileges of citizenship."

Lincoln responded that "the next Dred Scott decision" could allow slavery to spread into free states.

He said that it would be wrong for emancipated slaves to be treated as "underlings", but that there was a large opposition to social and political equality and that "a universal feeling, whether well or ill-founded, cannot be safely disregarded."

He asked Douglas to reconcile popular sovereignty with the Supreme Court's Dred Scott decision.

By allowing slavery where the majority wanted it, he lost the support of Republicans led by Lincoln, who thought that Douglas was unprincipled.

He lost the support of the South by rejecting the pro-slavery Lecompton Constitution and advocating a Freeport Doctrine to stop slavery in Kansas, where the majority were anti-slavery.

[31][32]In his subsequent response, Stephen Douglas said that Lincoln had an ally in Frederick Douglass in preaching "abolition doctrines."

Lincoln said that Chief Justice Roger Taney and Stephen Douglas were opposing Thomas Jefferson's self-evident truth, dehumanizing blacks and preparing the public mind to think of them as only property.

In Quincy, Lincoln said that Douglas's Freeport Doctrine was do-nothing sovereignty that was "as thin as the homeopathic soup that was made by boiling the shadow of a pigeon that had starved to death.

New railroads connected major cities at high speeds—a message that on a horse would have taken a week arrived in hours.

A forgotten "soft" technology, Pitman shorthand, allowed writing to keep up with speech, far closer to a recording than had been possible before.

"The combination of shorthand, the telegraph and the railroad changed everything," wrote Allen C. Guelzo, author of Lincoln and Douglas: The Debates That Defined America.

[41] In 2008, BBC Audiobooks America recorded David Strathairn (Lincoln) and Richard Dreyfuss (Douglas) reenacting the debates.