You must simultaneously believe:
That states passing laws to enforce existing federal immigration law violates Federal supremacy
Sanctuary cities and counties that ignore immigration law, and refuse to cooperate with ICE, do not violate federal supremacy.
Update, Feb 17, 2012:
This form of "believing the impossible" has a special name given to it by George Orwell: Doublethink:
To know and not to know, to be conscious of complete truthfulness while telling carefully constructed lies, to hold simultaneously two opinions which cancelled out, knowing them to be contradictory and believing in both of them, to use logic against logic, to repudiate morality while laying claim to it, to believe that democracy was impossible and that the Party was the guardian of democracy, to forget, whatever it was necessary to forget, then to draw it back into memory again at the moment when it was needed, and then promptly to forget it again, and above all, to apply the same process to the process itself -- that was the ultimate subtlety; consciously to induce unconsciousness, and then, once again, to become unconscious of the act of hypnosis you had just performed. Even to understand the word 'doublethink' involved the use of doublethink.
The evil involved is considerable.
And so is the mental effort.
This level of Liberalism requires an "Intellectual" - demonstrating, with stark clarity, the difference between "smart" and "wise".