Today we would call it judicial activism. Then, it was a precursor to civil war.
I think it was called "interpretation". Or even more simply, "reading". In this case, reading the Service clause of Article IV, Section 2. The Northern States had been practicing a form of nullification, and he broke their china, just as Andy Jackson had broken the Virginians' and Carolinians' china during the Nullification Crisis 25 years earlier.
Today we would call it judicial activism.
I disagree, I don't think he engaged in legal positivism to arrive at his conclusion.
Then, it was a precursor to civil war.
It was the trigger that forced Abraham Lincoln to choose one good over another. War was his policy, as I've said.