James M. McPherson, "Lincoln, Abraham," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00631.html.
Before 1854 Lincoln had said little in public about slavery, but during the next six years he delivered an estimated 175 speeches whose "central message" was the necessity to exclude slavery from the territories as a step toward its ultimate extinction everywhere (Waldo W. Braden, Abraham Lincoln: Public Speaker , pp. 35-36). That had been the purpose of the Founding Fathers, Lincoln believed, when they adopted the Declaration of Independence and enacted the Northwest Ordinance of 1787, barring slavery from most of the existing territories; that was why they did not mention the words "slave" or "slavery" in the Constitution. "Thus, the thing is hid away, in the constitution," said Lincoln in 1854, "just as an afflicted man hides away a wen or cancer" (Basler, vol. 2, p. 274). By opening all of the Louisiana Purchase territory to slavery, the Kansas-Nebraska Act had reversed the course of the Founding Fathers. That was why Lincoln was "aroused," he later recalled, "as he had never been before" (Basler, vol. 4, p. 67).