By reigniting the sectional flames, the Dred Scott case provided Republican politicians with fresh challenges and fresh opportunities. Abraham Lincoln had long since put behind him his hardscrabble log-cabin beginnings in Kentucky and Indiana. Now living in Springfield, Illinois, he earned good money as a lawyer, but politics was his life. “His ambition was a little engine that knew no rest,” observed his law partner William Herndon. Lincoln had served as a Whig in the Illinois state legislature and in the House of Representatives, but he had not held public office since 1849.

Convinced that slavery was a “monstrous injustice,” a “great moral wrong,” and an “unqualified evil to the negro, the white man, and the State,” Lincoln condemned the Kansas-Nebraska Act of 1854 for giving slavery a new life and in 1856 joined the Republican Party. He accepted that the Constitution permitted slavery in those states where it existed, but he believed that Congress could contain its spread. Penned in, Lincoln believed, plantation slavery would wither, and in time Southerners would end slavery themselves.

Lincoln held what were, for his times, moderate racial views. Although he denounced slavery and defended black humanity, he also viewed black equality as impractical and unachievable. “Negroes have natural rights … as other men have,” he said, “although they cannot enjoy them here.” Insurmountable white prejudice made it impossible to extend full citizenship to blacks in America, he believed. In Lincoln’s mind, social stability and black progress required that slavery end and that blacks leave the country.

Lincoln envisioned the western territories as “places for poor people to go to, and better their conditions.” But slavery’s expansion threatened free men’s basic right to succeed. The Kansas-Nebraska Act and the Dred Scott decision persuaded him that slaveholders were engaged in a dangerous conspiracy to nationalize slavery. The next step, Lincoln warned, would be “another Supreme Court decision, declaring that the Constitution of the United States does not permit a State to exclude slavery from its limits.” Unless the citizens of Illinois woke up, he warned, the Supreme Court would make “Illinois a slave State.”

In Lincoln’s view, the nation could not “endure, permanently half slave and half free.” Either opponents of slavery would arrest its spread and place it on the “course of ultimate extinction,” or its advocates would see that it became legal in “all the States, old as well as new — North as well as South.” Lincoln’s convictions that slavery was wrong and that Congress must stop its spread formed the core of the Republican ideology. In 1858, Republicans in Illinois chose him to challenge the nation’s premier Democrat, who was seeking reelection to the U.S. Senate.