There is a wide-spread and gross misunderstanding of the meaning and operation of “sanctuary city” when it comes to discussions of cities cooperating or not with federal immigration policies. Among those confused about the matter are sadly included many presidential candidates.
When we talk of sanctuary cities in the context of the current debate, the jurisdictions that fall into that vague label are not commanding their employees to sneak around back alleys in the dark of night and to furtively hide out people from pursuing immigration agents. The issue, the sole issue, is that those jurisdictions are refusing to use their people and jail facilities to serve federal immigration law purposes.
What the federal government generally wants is for state and local jailers and street cops to check the immigration status of the people they come in contact with and to hold them over and above the time authorized by the event that brought them into state contact, sometimes by 48 hours, so that immigration agents can attend to them. If the people so contacted are witnesses to crime, they need to know they will not be turned over to immigration agents once they have assisted local law enforcement solve a crime. If the people so contacted are in jail for their own state crime, they need to be released when their commitment to the state is over and not be held additional periods of time for federal agents to contact them – local jails cannot hold people beyond their lawful release time, and the jail overcrowding we have now sees many local detainees released early anyway – do we use that scarce space to enforce federal law when we don't have enough even for state law? Are we to command overworked local police to do searching background checks to decide if the people are here illegally? What if they guess wrong and the person is illegally held – does our polity want to cough up the civil damages for that?
So, these so-called sanctuary cities are jurisdictions in which local officials have decided that they will not assist federal immigration enforcement; they are local jurisdictions that refuse to implement a federal program, for various reasons. [I doubt constitutional purity is one of those reasons, but it is for me!]
Whether it is wise for those jurisdictions to go that way or not, it is perfectly legal, and actually constitutionally compelled, if anyone heeds the doctrine of federalism, which is as ingrained in our founding structure as is federal supremacy and immigration policy.
Although the Constitution decrees that federal law is supreme, it is only supreme in its appropriate sphere. The appropriate sphere reality means that the federal government may not commandeer state and local governments to implement laws that are of an exclusively federal nature, which immigration is. That means that the federal government may enforce federal laws regardless of the desires of state and local government [as we have seen with the questionable enforcement of federal drug policy against things that are legal in the states], but the federal government may not command state governments to enforce exclusively federal law. Indeed, it is questionable whether state governments can constitutionally enforce federal law even if it wants to, but that is another question.
As was held in Printz v. United States [where the subject is whether the states had to heed the federal policies of background checks for gun purchases, the answer being “no”]: “The Federal Government may neither issue directives requiring the States to address particular problems, nor command the States' officers, or those of their political subdivisions, to administer or enforce a federal regulatory program. It matters not whether policymaking is involved, and no case by case weighing of the burdens or benefits is necessary; such commands are fundamentally incompatible with our constitutional system of dual sovereignty.”
None other than Justice Scalia penned those fundamental words.
Unfortunately, the federal government does have strong-arm tactics that it can employ, which would be inconsistent with the Framers' intents about federalism, but which it has contra-constitutionally employed on many matters over the years, and that is the tax and spend authority that the Constitution set up. The federal government can over-tax people and then offer to dole out some of its ill-gotten booty back to the states via grants and other fiscal inducements, thereby giving the states a painful choice over policy matters that the federal government could not directly command. That is, the federal government could offer to not withhold grant moneys for state and local law enforcement activities and materiel if the state and local people would get on board the immigration requests. That is one of many instances in which government can practice policies that would get you or me thrown into prison, because that practice is common law blackmail!
Many local programs [even DUI checkpoints] are funded through the federal government, as are highway building projects, etc., and we have become so attached to the federal teat that we frequently lose sight of the fundamental doctrine of federalism.
So, the feds could say either cooperate or we will starve you, but fortunately they have not gone down that Constitution-busting road on this matter yet.
But those who claim or pretend to be lovers of the Constitution need to understand that there is nothing illegal nor unconstitutional about the “sanctuary city” practices of the nature discussed here, and there is much contra-constitutional about the federal government commanding the states to do their bidding.