I’m sure this is a captain obvious statement, but, it seems plain to me that the states not only have the Constitutional right, but the duty to refuse to obey un-Constitutional laws or actions taken by the federal government. This is not secession. It is not required.
I find the situation similar to being given an order in the military that violates the military code of conduct. The soldier is not required to follow that kind of order. He/she may get into lots of trouble and have to defend themselves in court, but they do not have to be “out of the military” in order to refuse to obey.
The question will remain - does the particular state refusing to follow a specific federal law on the basis of nullification have the political and moral will to follow it through to the end? I hope the answer is “yes”.
A point that needs to be clarified more often: refusal to bow to every federal mandate that comes out of the Congressional hat does not = secession.
There may be other issues / problems invovled, but an assertion of state sovereignty in relation to a particular act of the federal government is nowhere near the same as secession.