Since Donald Trump’s victory in the 2016 election, “sanctuary” jurisdictions have become a focus of political and legal controversy. Sanctuary policies are adopted by state and local governments that refuse to aid federal officials in enforcing certain federal laws. They can be thought of as attempts to build a type of legal wall around a state or municipality.

For example, in Trump’s first term, immigration sanctuaries forbade local law enforcement organizations from helping to enforce some federal immigration laws. Those policies have been imitated by conservative states passing gun-sanctuary laws. In the future, especially if Trump returns to power, we may well see controversy over other types of sanctuaries, such as state and local governments seeking to protect abortion rights.

Sanctuary policies have their flaws and limitations. But they have strong constitutional grounding and are a useful check on federal power, especially on overreaching presidents of both parties. So it is worth exploring how sanctuary policies work and their constitutional foundations.

What Sanctuary Policies Are
Sanctuary policies are laws and regulations adopted by state and local governments that deny assistance to federal officials seeking to enforce particular federal laws. Currently, the most widespread sanctuary policies are left-liberal immigration sanctuaries. Over the last 20 years, numerous liberal “sanctuary cities” and “sanctuary states” have adopted policies barring their law enforcement agencies from assisting in the deportation of many categories of undocumented immigrants—usually those not convicted of serious crimes. Depending on how we count, there are either 11 or 12 immigration “sanctuary states,” and dozens of local governments with similar policies.

In recent years, left-wing immigration sanctuaries have been imitated by conservative gun sanctuaries, beginning with Montana. Gun sanctuary laws—or “Second Amendment Protection Acts,” as advocates like to call them—deny cooperation with enforcement of a variety of federal gun control laws. Three states—Idaho, Missouri, and Wyoming—have full-blown gun sanctuary laws, thereby earning a “gold” rating from Gun Owners of America (a pro-gun rights advocacy group). Seven other red states have more limited legislation.

Sanctuary laws are often analogized to “nullification”—the idea that states can render federal laws null and void within their territory. Nullification, of course, has a terrible reputation because of its association with southern states’ defense of slavery and (later) segregation. But there is an important distinction between sanctuary laws and nullification.

Nullificationists argue that the federal laws in question are completely void, and that states have the right to actively impede their enforcement on their territory. By contrast, sanctuary jurisdictions do not necessarily claim the laws in question are void. They merely deny them the assistance of state and local governments, particularly law enforcement agencies. For example, they refuse to help enforce the relevant laws themselves, or to provide information to federal law enforcement agencies engaged in enforcement efforts. But the feds remain free to try to enforce these laws using only their own resources and personnel.

In this respect, sanctuary jurisdictions are not actually complete sanctuaries. Undocumented immigrants protected by immigration sanctuaries may still be caught and deported by Immigration and Customs Enforcement (ICE) or other federal agencies. Gun owners protected by gun sanctuaries may, similarly, be apprehended by federal law enforcement agencies, such as the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). Federal prosecutors remain free to charge violators of these laws in federal court.

Nonetheless, sanctuary jurisdictions’ denial of state and local assistance to federal law enforcement makes a difference. In the U.S. federal system, some 90% of law enforcement personnel are state and local government employees; only about 10% work for the federal government. Because of this imbalance, federal law enforcement agencies are heavily dependent on state and local cooperation to effectuate enforcement of most federal laws. When states and localities deny such assistance, it becomes extremely difficult for federal law enforcement to catch more than a small fraction of violators. This is particularly true of laws—including both immigration and gun laws—where the number of violators is very large. For example, there are some 11 million undocumented immigrants in the country. For these reasons, sanctuary policies significantly reduce the enforcement of federal laws they target, even if they cannot eliminate such enforcement entirely.

Abortion: A Potential New Sanctuary Frontier
While immigration and gun laws have been the main focus of sanctuary policies over the last decade or so, that could change. In the wake of the Supreme Court’s ruling in Dobbs v. Jackson Women’s Health Organization (2022), overturning Roe v. Wade, several liberal states have enacted “abortion shield” laws that protect medical providers and others who perform abortions for women from states with laws banning or severely restricting abortions. They also protect providers of abortion pills and related services.

While these laws primarily bar state cooperation with law enforcement by other states (in this case, states with abortion bans), they could also be used or expanded to bar cooperation with federal law enforcement as well.

Many Republicans advocate a national abortion ban, possibly one focused on abortions after 15 weeks of pregnancy. While Donald Trump (probably fearing adverse electoral consequences) has thrown some cold water on the notion, it could easily be resuscitated if he wins the presidency and the GOP also has control of both houses of Congress. Other conservatives involved in planning a potential new Trump administration want to use the archaic 1873 Comstock Act as a tool to ban shipment of all abortion-related equipment and medications, thus potentially leveraging that law into a nation-wide abortion ban. Whether courts would accept such a gambit is uncertain.

If either new federal legislation or the Comstock Act are used to impose nationwide abortion restrictions, we are likely to see abortion sanctuaries comparable to immigration and gun sanctuaries. Many blue states would almost certainly refuse to assist with enforcement of such laws. Adverse federal action on marijuana legalization or other issues could also potentially trigger state resistance through sanctuary policies.

The Constitutional Basis for Sanctuary Laws
Constitutional protection for sanctuary jurisdictions rests on a series of Supreme Court decisions holding that the 10th Amendment—which states that “powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States … or to the people”—bans federal “commandeering” of state governments. The leading decisions to that effect are New York v. United States (1992), and Printz v. United States (1997). They hold, among other things, that state and local governments cannot be compelled to help enforce federal law. The anti-commandeering doctrine was further extended in Murphy v. NCAA (2018), which held that the federal government cannot issue orders to state legislatures and thereby force states to enact legislation or to refrain from repealing state laws.

Critics often claim that the Supreme Court’s anti-commandeering jurisprudence has no basis in the text and original meaning of the Constitution. But, as legal scholar Michael Rappaport showed in an important 1999 article, the anti-commandeering decisions have a basis in the Founding-era understanding of the word “state,” which implied a sovereign authority that the federal government could not undercut by seizing control over the state’s government apparatus.

Printz and New York were decided by mostly conservative Supreme Court justices over vociferous dissents by the Court’s liberals. The law at issue in Printz required local officials to enforce a new federal background check gun law opposed by conservatives. Murphy was a 7–2 decision authored by conservative Justice Samuel Alito, with two liberal justices in dissent.

Ironically, these conservative decisions have been most extensively used by liberal immigration sanctuaries to successfully fend off Trump administration efforts to force them to aid the deportation of undocumented migrants. In the Trump era, liberal states and migrant-rights activists learned to love—or at least make use of—conservative federalism precedents they had previously opposed.

During Trump’s term in office, his administration reviled sanctuary cities and sought to bring them to heel as much as possible. The anti-commandeering rule precluded efforts at direct coercion. It led courts to largely reject a Trump lawsuit seeking to overturn California’s “sanctuary state” law.

The extension of the doctrine in Murphy prevented the administration from making effective use of 8 USC Section 1373, a federal law barring state and local governments from instructing their employees to refuse to share information on undocumented immigrants with federal law enforcement agencies. Multiple lower court decisions ruled that Murphy either required the invalidation of Section 1373 or compelled judges to interpret it very narrowly, rendering the law essentially ineffective. While Murphy struck down a federal law restricting states’ abilities to legalize sports gambling, its biggest practical impact was to give legal support to the idea of liberal immigration sanctuaries.

The Trump administration also tried to pressure sanctuary cities by threatening to cut off federal grants. A 2017 executive order tried to withhold nearly all federal funds to states and localities that refused to obey Section 1373. Later, the Department of Justice attempted to deny certain law enforcement grants to jurisdictions that refused to meet several immigration-enforcement-related conditions.

Both policies were struck down by federal courts because they violated Supreme Court precedent limiting the use of the spending power to coerce state and local governments. The Court had previously held that grant conditions must be clearly spelled out in the relevant statute; they must be related to the purpose of the grant and could not be so sweeping as to be “coercive.” Thus, for example, the federal government couldn’t withdraw all education funding to get states to enforce its immigration laws—that would be both non-related and coercive. The Trump policies were held to violate the requirement of clarity; indeed, they effectively sought to usurp Congress’s power over federal spending by imposing new conditions created by the executive branch. Courts also ruled that the executive order violated the anti-coercion rule because it covered such a vast range of grants. Some court decisions further concluded that Trump’s conditions violated the “relatedness” requirement.

Like the anti-commandeering rule, precedents limiting the use of the federal spending power had been pioneered by conservative justices and opposed by many liberals (though not as uniformly). But the sanctuary cases shifted their ideological valence.

After Trump’s 2020 defeat, Joe Biden and Attorney General Merrick Garland put an end to most of Trump’s anti-immigration-sanctuary policies. But the new administration was hostile to conservative gun sanctuaries. While it did not launch an extensive campaign against them on the scale of Trump’s effort to coerce immigration sanctuaries, the Biden DOJ did file a dubious lawsuit challenging the Missouri gun sanctuary law. In March 2023, a federal district court issued a badly flawed decision, ruling against the Missouri law. The judge recognized that the federal government cannot force Missouri to aid in the enforcement of federal gun laws but wrongly argued that the state law went beyond merely withholding assistance. In reality, the Missouri law does no such thing; hopefully, the ruling will be reversed on appeal.

While sanctuary policies enable states to deny assistance to federal efforts to enforce laws against private parties, it is important to recognize that they do not empower states to violate federal laws themselves. States cannot use such policies to prevent the federal government from, for example, suing them for violating citizens’ constitutional rights. Nor can they use sanctuary laws to eliminate constitutional rights directly.

Legal and political conflict over sanctuary laws is likely to continue in the future. Should Trump prevail in the 2024 election, a second Trump administration plans to engage in a massive deportations of undocumented immigrants and would almost certainly make a renewed effort to coerce immigration sanctuaries. Hopefully, these will run afoul of the same constraints that undermined first term efforts.

If Trump is backed by GOP majorities in both houses of Congress, the Republicans could also try to enact new laws trying to use the spending power to pressure sanctuaries—for example, by tying a wide range of federal grants to immigration enforcement. Depending on how such laws are structured, they might run afoul of constitutional constraints.

As already discussed, a GOP administration might also clash with blue states over abortion. If a Republican president tries to use the Comstock Act to impose nationwide abortion restrictions, or new restrictions are enacted by Congress, blue states are likely to use “shield” laws to deny cooperation. The same applies if Congress were to enact a federal law restricting interstate travel to get an abortion.

Should President Biden be reelected, the Department of Justice case against the Missouri gun sanctuary law is likely to continue. The administration might also target other gun sanctuaries. More generally, both red and blue states might, in the future, try to use sanctuary laws against federal regulations on various issues. Immigration, guns, and abortion are far from the only situations where states might want to refuse to help enforce federal laws they object to.

Sanctuaries as a Check on Authoritarianism
Politicians’ and activists’ positions on sanctuary laws often reek of “fair weather federalism.” Their stances depend on whose ox is being gored. Supporters of immigration sanctuaries oppose gun sanctuaries, and vice versa, even though the constitutional issues in the two types of cases are very similar.

But there are good reasons to support state and local rights to adopt sanctuary policies that go beyond one’s specific policy preferences. If the federal government has broad power to force states to do its bidding, that power could easily be abused—especially in an era where there is severe ideological polarization, and many on both sides of the political spectrum are eager to coerce their adversaries.

The danger is heightened by the ways in which such power is likely to be concentrated in the hands of the executive. If the president can use vaguely worded laws to attach new conditions to federal grants, as Trump tried to do, he could easily use that to consolidate power and impose his own preferences on unwilling states and localities.

The case for sanctuary policies is even stronger if you fear that Trump—or some other potential future president—has authoritarian tendencies. Sanctuary jurisdictions can make such authoritarian aspirations harder to realize by giving refuge to the would-be dictator’s opponents.

Even when there is no authoritarian threat looming, sanctuary policies play a valuable role in preserving diversity in our federal system. In a highly diverse nation like the U.S., federally imposed uniformity would deny millions of people the opportunity to live under policies they prefer.

Sanctuary policies also help empower people to “vote with their feet” for the policies they prefer. People who dislike their home state’s policies on immigration, guns, or some other issue, have the opportunity to relocate to a more congenial jurisdiction. Where authority devolves to local governments, foot-voting opportunities are even greater, as it is often cheaper and easier to move between local governments than between states.

Foot voters generally make better-informed decisions than ballot-box voters do. In addition, the former can exercise greater freedom of choice than the latter, because their decisions are far more likely to decisively determine what laws they live under. In most elections, a ballot-box voter has only an infinitesimally small chance of decisively affecting the outcome (about 1 in 60 million in a presidential election, for example). Foot voters have much greater leverage.

Worth the Trade-Off
Sanctuary policies do have the downside that they could potentially be used to weaken enforcement of valuable federal laws. But this danger is readily outweighed by the benefits of checking federal power, preserving diversity, and empowering people to vote with their feet.

Some might argue that sanctuary policies are objectionable because they impede effective enforcement of many federal laws. That violates the seeming principle that every duly enacted law must be fully enforced. But we already have far more laws—and law-breakers—than any enforcement apparatus can hope to deal with. The majority of adult Americans have violated federal criminal law at some point in their lives, to say nothing of state law and civil law.

In such circumstances, government officials inevitably exercise extensive discretion over which laws to enforce and to what degree. It makes sense to allow some of that discretion to be used to deny state assistance for the enforcement of federal laws that the state and its people disapprove of. That puts a check on federal power, promotes diversity, and empowers more people to vote with their feet.

Ideally, we should reduce law-enforcement discretion by cutting back on the number of laws. But unless and until that happens, sanctuary policies are a good way to use some of the discretion that unavoidably exists.