There are grave misunderstandings about the meaning and practices of “sanctuary cities.” Certain uber-right reactionaries, who generally claim to revere the Constitution, falsely claim that the practice is illegal [Rush Limbaugh said exactly that on his show recently], and the term “sanctuary” invites some to harken back to the olden days when Catholic and other churches took affirmative steps to hide people out so the bad guys of government or whatever could not find them.
The modern urban practice labeled “sanctuary city” means merely that local and state executive officials refuse to assist the federal government to enforce federal law, particularly immigration law. And that is a constitutionally sound position to take – as sound as the expansive Second Amendment positions espoused by those who criticize the “sanctuary” practice. If you are a true constitutionalist, you have to eagerly embrace all of the fundamental law, not merely the aspects that you have cherry picked to satisfy your biases.
Remember that when certain states tried to enact laws against illegal immigrants, the feds came in and told them to back off because immigration policies are exclusively federal – the states have no business sticking their noses into the subject matter, and the Supreme Court agreed with the feds. Bingo! Immigration policies are exclusively federal; the states have no role, and hence no duty.
And things that are exclusively federal cannot be forced onto the states under well-established doctrines of federalism and under the correlative doctrine that the national government may only do that which is expressly authorized by the Constitution, generally in Article 1, section 8. That is, the states' executive authorities cannot be commandeered by the federal government to enforce federal law.
That being the case, and it is the constitutional law of the matter, people should not be hoodwinked by reactionary red meat eaters into thinking the states and their cities are somehow violating federal law, because they are not.
There are also public policy rationalizations that have impelled some of the municipalities to embrace the practice, one in particular that victims of crimes who are here illegally might be less likely to report crimes and cooperate with the police in various investigations if there was the possibility that their cooperation would result in them being turned over to immigration authorities. But that is the rationalization for embracing the policy, it is not the constitutional ground for the existence of the policy, which finds its roots in the 10th Amendment, coupled with the limits found in Article 1, section 8.
Indeed, for those supposed “conservatives” who think it is some liberal social engineering that prevents the feds from commandeering state executives into enforcing federal law, you might be interested in the wonderful Scalia opinion on the subject in Printz v. United States (1987) 521 U.S. 898 [“Finally, and most conclusively in these cases, the Court's jurisprudence makes clear that the Federal Government may not compel the States to enact or administer a federal regulatory program”]. That holding was over liberal opposition.
So, those who promote the notion that the feds can command executive authorities of the states to enforce federal law are adopting the liberal position, not the originalist conservative position. Rush, Bannon, Trump, take note: Sanctuary Cities find constitutional sanctuary in the Originalist Constitution; if you disagree, you are a liberal, or ignorant!
Some have retorted that the feds should just withhold funds from the states until they cooperate! The federal grant program, whereby the feds heavily tax states' citizens and then dole a small percentage back if the states get on board federal programs is sheer extortion that the Framers would be appalled about - it is a contortion of the federal Tax and Spend Clause, wherein the feds extort cooperation regarding matters that they cannot directly command by threats about withholding that which they should not have seized. If a regular citizen practiced such, he would be in prison. It is another Constitution-busting doctrine that the liberals pressed: true originalists would never tolerate that invasion of state sovereignty. But the Tax and Spend Clause does not enable the federal government to command state executives to do anything; read Printz to garner greater understanding re commandeering. Read extortion articles to understand why the feds cannot legitimately command illicit things on threat of taking money for non-compliance. Then too, see NFIB v. Sebelius (2012) --- U.S. ---, --- [132 S.Ct. 2566, 2602]: federal legislation that coerces a state to adopt a federal program as its own as a condition of receiving grant moneys violates fundamental federalism principles. Quite simply, under the Tenth Amendment, “The Federal Government may not compel the States to enact or administer a federal regulatory program.” New York v. United States (1992) 505 U.S. 144, 188.
So, hey, supposed conservatives, supposed constitutionalists, supposed "originalists," you want to embrace liberal doctrines repugnant to the intent of the Framers to effectuate your latent [and not so latent] racism? If you are a true conservative, a devotee of constitutional originalism, you support sanctuary city practices. If you are a liberal or a police power reactionary [called Fascist in earlier times], you do not. You choose what bed you lie in. And then adjust the firmness.