They get to ignore all the unconstitutional ones. In fact, thay have an obligation to do so, but they are too cowardly or greedy to fulfill their obligation.
Believe me, I'm all in favor of the Constitution. But my understanding of our system is that the courts, and not the states, ultimately decide on the constitutionality of laws. And defending our country's borders is not only a constitutional mandate, it's supposed to be one of the government's top priorities.