Did Stephen Douglas enforce popular sovereignty?

No.

'Popular Sovereignty' was a successful slogan for his plan to allow new states to decide whether to be slave or free, by a local vote.

He got the Kansas-Nebraska Act through Congress, but Popular Sovereignty turned out to be quite unworkable, because only one state could vote at a time, and every bully-boy in America would descend on that one state, to cause maximum mayhem.

The experiment would not be tried again.