In 1858, it seemed conceivable that Stephen Douglas might assume leadership of an extremely moderate, mainstream antislavery cause. During the debates, Lincoln sought to portray Douglas as indifferent to the moral evil of slavery, and therefore disqualified from leading an antislavery coalition.
Lincoln on the "Ultimate Extinction" of Slavery, Extract form Mr. Lincoln's Jonesboro speech, delivered September 15, 1858:
...[Stephen Douglas] says, "Why can't this Union endure permanently, half slave and half free?" I have said that I supposed it could not, and I will try, before this new audience, to give briefly some of the reasons for entertaining that opinion. Another form of the question is, "Why can't we let it stand as our fathers placed it?" That is the exact difficulty between us. I say that Judge Douglas and his friends have changed them from the position in which our fathers originally placed it. I say in the way our fathers originally left the slavery question, the institution was in the course of ultimate extinction, and the public mind rested in the belief that it was in the course of ultimate extinction. I say when this government was first established it was the policy of the founders to prohibit the spread of slavery into the new territories of the United States, where it had not existed. But Judge Douglas and his friends have broken up that policy and placed it upon a new basis by which it is become national and perpetual. ALL I HAVE ASKED OR DESIRED ANYWHERE IS, THAT IT SHOULD BE PLACED BACK AGAIN UPON THE BASIS THAT THE FATHERS OF OUR GOVERNMENT ORIGINALLY PLACED IT UPON. I have no doubt that it would become extinct, for all time to come, if we but re-adopted the policy of the fathers by restricting it to the limits it has already covered--restricting it from the new territories.…