Answer:
Lincoln successfully defended the principle of popular sovereignty.
Step-by-step explanation:
They were also known as the Great Debates of 1858. They were seven debates held between the candidate for Senator of Illinois, Abraham Lincoln and the incumbent Senator, Stephen Douglas. The main issue discussed in the debates was slavery.
Douglass was the one who defended the principle of popular sovereignty, this was letting the people of a territory decide for themselves whether to allow slavery or not. Lincoln was against it because he said that popular sovereignty would perpetuate slavery.
I hope this answer helps you.