A leader of the Democratic Party, Douglas had made himself politically vulnerable when he broke with Democratic President James Buchanan and southern Democrats over the issue of Kansas statehood. Douglas opposed the admission of Kansas as a slave state under the terms of the controversial, proslavery Lecompton constitution. That constitution, which was widely believed to have been the result of voter fraud by Missouri border ruffians, would have legalized slavery in the new state. Douglas, hoping to appeal to antislavery northern Democrats and Republicans, took a popular sovereignty stance and opposed the constitution as unrepresentative of the majority opinion in Kansas. Enraged southern Democrats accused Douglas of party treason.
Lincoln understood that he would have to take a high moral ground to undermine the temptation of some Republicans to vote for Douglas as a means of dividing the national Democratic Party. To this end, Lincolns campaign began with his famous House Divided Speech delivered in Springfield, Illinois, on June 16, 1858. Recognized as one of the most important speeches in American history, his powerful message warned that the crisis over slavery would not be resolved until the nation stood either completely slave or totally free. A house divided against itself cannot stand, he declared, in prophetic words that supported the irrepressible conflict doctrine. He then turned on Douglas by saying that the threat to the nations unity came principally from Douglass popular sovereignty perspective. Lincoln envisioned a dozen Bleeding Kansas episodes in which settlers fought over the issue of slavery in order to get the upper hand in the territories.