What Supreme Court precedents govern state refusal to enforce federal law, and how do they apply to sanctuary policies?

1. The core precedents: anti‑commandeering and spending‑power limits

The Supreme Court’s anti‑commandeering doctrine—grounded in the Tenth Amendment—holds that the federal government cannot compel state legislatures or officers to implement or enforce federal regulatory programs, a principle anchored in New York v. United States and reaffirmed in Printz v. United States and later cases such as Murphy v. NCAA ^{[1] [2] [3]}. Separate but related is the Court’s constraint on the spending power: the federal government cannot coerce states through conditioning of federal grants in ways that effectively commandeer state policymaking, a line of authority courts have relied on to block executive efforts to cut off broad categories of federal funding to non‑cooperating jurisdictions ^{[4] [2]}. Those twin doctrines form the constitutional floor for most modern judicial decisions that protect state and local prerogatives from federal commands ^[3].

2. How those precedents have been applied to sanctuary policies

Courts have read the anti‑commandeering rule to permit cities and states to adopt “sanctuary” measures that refuse to assist federal immigration enforcement—by declining to honor ICE detainers or sharing certain information—because those policies do not nullify federal law but simply withhold state assistance, which the Constitution allows ^{[4] [3]}. Federal efforts to punish noncompliance by withholding unrelated federal funding have been rebuffed where courts found the conditions coercive or untethered to the grant program’s purpose, sustaining sanctuary jurisdictions against some Trump‑era and subsequent federal sanctions ^{[4] [7]}. At the same time, the Supremacy Clause means state laws that directly regulate immigration or conflict with federal statutes remain vulnerable to preemption; courts therefore distinguish between non‑cooperation and affirmative state regulation of immigration ^{[3] [8]}.

3. Doctrinal limits and contested statutes: §1373, detainers, and criminal exposure

Several contested federal moves test doctrinal edges: Congress’s use of Section 1373 and similar statutes to forbid local restrictions on sharing immigration information has generated litigation because courts and commentators disagree whether such statutes amount to impermissible commandeering or valid preemption; appellate panels and observers have expressed doubt about §1373’s constitutionality even as some actors argue it expressly preempts contrary state measures ^{[9] [5]}. Courts have also held that ICE detainer forms are not compulsory commands that automatically bind local law enforcement, and criminal statutes like the harboring statute (8 U.S.C. §1324) have typically required active concealment or deception rather than mere refusal to cooperate—meaning criminal liability for honoring sanctuary policies has so far been legally uncertain and rarely pursued ^{[10] [6] [5]}.

4. Political stakes, litigation strategy, and what’s unresolved

The legal architecture produces predictable litigation strategies: federal plaintiffs press preemption and punitive‑funding theories while jurisdictions rely on anti‑commandeering and spending‑clause protections, and both sides tailor factual records to tilt circuits ^{[7] [11]}. Observers caution that Supreme Court composition and shifting doctrinal emphases could invite reexamination of precedents that sanctuary advocates now rely on, and executive branch memos threatening prosecutions or funding cuts are likely to spawn more suits testing whether policy tools cross constitutional lines ^{[11] [6]}. Reporting and legal analyses show current doctrine protects the right of states and cities to decline assistance with federal immigration enforcement, but the contours of coercion, preemption, and statutory reach—especially regarding §1373, narrow criminal statutes, and targeted funding conditions—remain open and litigated ^{[4] [5] [9]}.