The Moral Lights

As Stephen Douglas staggered under alcohol, illness and the repetition of old ideas, Abraham Lincoln found the clear distinction between them in their debates -- and hammered his opponent pitilessly over his indifference to slavery.

Sources used:

Blumenthal, Sidney: All The Powers of Earth. Simon and Schuster, 2019.
 
Burlingame, Michael, Abraham Lincoln: A Life. (Vol. 1). The John Hopkins University Press, 1995.

Collected Works of Abraham Lincoln. 1953 Edition hosted by the University of Michigan.

Davis, Rodney and Wilson, Douglas, ed. Herndon's Informants: Letters, Interviews, and Statements about Abraham Lincoln. University of Chicago Press, 1998.
 
Davis, Rodney and Wilson, Douglas, ed. Herndon on Lincoln: Letters. Knox College Lincoln Studies Center, 2016.

Davis, Rodney and Wilson, Douglas, ed., The Lincoln-Douglas Debates. Knox-College Lincoln Studies Center, 2008.

Donald, David Herbert, Lincoln: A Biography. Simon and Schuster, 1995.

Foner, Eric, The Fiery Trial:  Abraham Lincoln and American Slavery. W.W. Norton and Company, 2011.

Guelzo, Alan, Lincoln and Douglas: The Debates That Defined America. Simon and Schuster, 2008.