It was Lincoln's successors who ruled under a version of the Constitution heavily amended by the 13th, 14th and 15th Amendments, but the 14th was the key. I wasn't actually referring to Lincoln in that sentence.
Remember, I'm only summarizing an essay I read that I can't find anymore.
Had you heard of the "sine die" issue and Lincoln's EO's? It's not info that's easily found...requires a lot of digging. Also, what's your take on the 14th Amendment...lots of discussion out there that it helped to undermine our citizenship rights.