I was reading an article about attorney general Jeff Sessions addressing the state of California regarding the state's recent laws on immigration. In summary, these laws make it illegal for a private business to cooperate with ICE, further clarifying the state as a so called "sanctuary" for illegal immigrants. Sessions' words left me with the impression that the American Civil War created ongoing legal implications that could be applied in a case against California. His words were:
"I understand that we have a wide variety of political opinions out there on immigration. But the law is in the books and its purposes are clear and just," Sessions said during a speech to the California Peace Officers' Association in Sacramento on Wednesday.
"There is no nullification. There is no secession. Federal law is the supreme law of the land. I would invite any doubters to go to Gettysburg, to the tombstones of John C. Calhoun and Abraham Lincoln. This matter has been settled."
Source
I understand the great ways the civil war changed the country, but this is honestly the first time that I've heard it invoked as if it was a legal precedent. Am I understanding Sessions' words correctly, or is he speaking more rhetorically than legally? More broadly, in what ways can the Civil War be cited as a political or legal point?