Courts & Litigation Foreign Relations & International Law

Immigration is Not Invasion

Ilya Somin
Monday, March 25, 2024, 8:00 AM
Texas’s argument equating the two goes against the text and original meaning of the Constitution, and would set a dangerous precedent if courts accept it.
U.S. Border Patrol agents follow "sign" as they patrol vast ranch-lands near Hebbronville, Texas, March 8, 2019 (Glenn Fawcett,; Public Domain)

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In two important cases currently before the U.S. Court of Appeals for the Fifth Circuit, the state of Texas has advanced the argument that illegal migration and drug smuggling qualify as an “invasion” authorizing the state to “engage in war” in response, under Article I of the Constitution. So far, federal courts have uniformly rejected such claims. But if they were to accept them, drastic consequences would follow. Border-state governments would be empowered to attack neighboring countries, even without congressional authorization. And the federal government would have the power to suspend the writ of habeas corpus—thereby detaining people without due process—almost anytime it wants. In addition to these practical considerations, Texas’s “invasion” argument is at odds with the text and original meaning of the Constitution.

In United States v. Abbott the federal government is suing Texas for installing floating buoy barriers in the Rio Grande to block migration and drug smuggling, thereby creating safety hazards and possibly impeding navigation. (I have authored an amicus brief in United States v. Abbott on behalf of myself and the Cato Institute.) The Biden administration claims this violates the Rivers and Harbors Act of 1899, which bars “[t]he creation of any obstruction not affirmatively authorized by Congress, to the navigable capacity of any of the waters of the United States.” In United States v. Texas, the state is defending the legality of S.B. 4, a new state law that criminalizes unauthorized migration, expands state law enforcement officials’ powers to detain undocumented migrants, and gives Texas state courts the authority to order removal of migrants convicted under the law. The federal government claims S.B. 4 is preempted by federal law and that it infringes on federal authority over immigration.

In both cases, Texas argues the federal government’s interpretation of the relevant statutes is wrong. But, more importantly, the state also contends that the Invasion Clause of Article I of the Constitution gives it the power to install buoys in the river border it shares with Mexico and to enforce S.B. 4 even if federal statutes forbid such actions. Article I, Section 10, Clause 3, of the Constitution states that “[n]o state shall, without the Consent of Congress, ... engage in war, unless actually invaded, or in such imminent Danger as will not admit of delay.” Texas claims illegal migration and drug smuggling qualify as “invasion” and that, therefore, the Constitution gives the state the power to take military action in response in defiance of federal statutes, and even in the absence of congressional authorization for war.

So far, courts have uniformly rejected this argument. In United States v. Abbott, federal District Judge David Alan Ezra (a Reagan appointee) wrote a strong opinion repudiating Texas’s “breathtaking” claim of authority. His ruling was affirmed by a three-judge panel of the U.S. Court of Appeals for the Fifth Circuit but is now up for en banc review before the full Fifth Circuit

In the S.B. 4 case, which was also litigated before Judge Ezra, he wrote the most thorough judicial opinion on the definition of “invasion” in all of American history. As he explains, the idea that illegal migration qualifies as invasion flies in the face of the text, history, and original meaning of the Constitution. The case is now on appeal to the Fifth Circuit. The Supreme Court recently allowed S.B. 4 to go into effect by refusing to lift an administrative stay that had been blocking the district court injunction against the law. But, within hours, the Fifth Circuit lifted the stay, thereby ensuring that S.B. 4—for now—cannot be enforced, as appellate review proceeds.

Previously, three federal appellate court rulings—all decided in the 1990s—also rejected the kind of argument advanced by Texas, holding that only an armed attack, not mere illegal migration, qualifies as “invasion.” Many courts have also held that the definition of “invasion” is a “political question” not subject to judicial review.

The Text and Original Meaning of “Invasion”

The constitutional text undermines the idea that “invasion” includes illegal migration and smuggling. The Invasion Clause relied on by Texas allows states to “engage in war” in response. That suggests an “invasion” must be the kind of organized assault that would normally justify full-scale war in response, including sending troops to attack and occupy the country from which the invasion originated. Illegal migration and smuggling do not qualify as such under international law, either today or at the time of the founding of the United States.

The Guarantee Clause of Article IV of the Constitution states that the federal government must protect the states “against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.” Here, invasion is paired with “domestic Violence”—which in 18th century usage refers to uprisings against the state government, not the modern use of the term to denote violence in family and intimate relationships. Under the long-standing doctrine of noscitur a sociis, “a word may be known by the company it keeps.” Here, it makes little sense to assume that “invasion” includes nonviolent actions, when it is coupled with “domestic Violence.”

The original meaning reinforces the text. As legal scholar Frank Bowman notes, “[T]hroughout the Constitutional Convention and the state ratification debates that followed, delegates and commentators used the term ‘invasion’ over and over” in ways that, with rare exceptions for “metaphorical” uses, “invariably refer… to a hostile armed incursion into or against the territory of the states or the nation.” 

In his Report of 1800, James Madison, one of the leading framers of the Constitution, responded to claims that the Guarantee Clause authorized the notorious Alien and Sedition Acts of 1798 by emphasizing that “[i]nvasion is an operation of war,” and thus the Clause does not authorize restrictions on immigration. The same logic applies to the use of “invasion” in Article I. Efforts to use other statements by Madison to support Texas’s position ignore the one time he specifically addressed the meaning of “invasion” and misinterpret those other statements, to boot.

There is some founding-era evidence suggesting that a relatively small invasion might have been enough to trigger the Invasion Clause. But a small invasion must still be an armed attack. Moreover, the possibility that a small invasion is sufficient for a state to qualify as “actually invaded” further undercuts Texas’s argument. If illegal migration or drug smuggling are invasions triggering the power to engage in war in response, and even a small invasion qualifies, that suggests that even small-scale illegal migration or smuggling would be sufficient to enable a state to wage war without congressional authorization. Such an absurd implication goes well beyond the ordinary meaning of the terms and certainly was not expected by anyone at the time of the founding.

Defenders of Texas’s position cite founding-era dictionaries that included metaphorical secondary definitions of “invasion,” as in the case of an “invasion” by a disease or an “invasion” of rights by an incursion. But there is no evidence the original understanding of the invasion provisions of the Constitution included such secondary meanings. As the district court noted in the S.B. 4 case, in interpreting terms in statutes and the Constitution, words must be given their “natural or normal meaning, not the broadest possible meaning.” In context, the natural meaning here is an organized armed attack on the United States.

In addition, as Justice Antonin Scalia emphasized in his opinion for the Court in District of Columbia v. Heller (2008), a major Second Amendment case, courts must prefer ordinary meaning over “secret or technical meanings that would not have been known to ordinary citizens in the founding generation.” In the context of Article I and Article IV, where “invasion” and “actually invaded” are used to denote actions that would justify engaging in war, or pose threats comparable to those of “domestic Violence,” ordinary citizens would not assume that mere unauthorized migration or smuggling qualify as invasions allowing such drastic responses.

It is also important to recognize that an “invasion” does not exist merely because some small percentage of immigrants and drug smugglers are armed. In any large group of people, there will almost always be a few who may carry weapons. Such a situation does not constitute an “invasion” unless they are actually engaged in a significant organized assault on the United States, as opposed to merely carrying arms for self-defense or in order to engage in ordinary criminal activity.

Dangerous Implications

If Texas prevails on its “invasion” argument, it would have dangerous implications that go far beyond allowing the state to place water buoys in the Rio Grande, or adopt measures like S.B. 4.

If border states can “engage in war” in response to illegal migration or drug smuggling, they would have the authority to attack neighboring nations at virtually any time. Ever since the federal government enacted significant restrictions on migration across the southern border in the early twentieth century (later expanded to include most migrants from Latin America), unlawful migration and cross-border drug smuggling has occurred virtually every year (though there was relatively little illegal migration during the Great Depression). If such activity qualifies as an invasion, Texas and other border states would be empowered to wage war in response, virtually any time they want. As the district court noted in the water buoy case, “Under this logic, once Texas decides, in its sole discretion, that it has been invaded, it is subject to no oversight of its ‘chosen means of waging war.’”

 Prominent conservative legal scholar John Yoo, a border hawk, warns that Texas’s argument would allow states to “attack drug-cartel members not only across the border but all the way back to their hideouts,” thereby triggering large-scale hostilities with Mexico. “Preventing states from provoking such conflicts,” he writes, “was the very purpose of Article I, Section 10’s bar on state war-making.”

Concerns about such escalation are more than just theoretical. Over the past year, the idea of turning the “war on drugs” into a real war by invading Mexico has become increasingly popular in GOP circles, advanced by a variety of prominent politicians, including Donald Trump. The risk of conflict becomes greater if a state like Texas can initiate it on its own, without federal authorization.

In addition to giving states the power to start wars without congressional authorization, Texas’s argument would give the federal government the power to suspend the writ of habeas corpus almost any time it wants, thereby enabling detention of suspects without trial or filing charges. The Suspension Clause of the Constitution states that “[t]he Privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it” (emphasis added). If illegal migration and drug smuggling qualify as “invasion” for purposes of triggering state and federal authority to resist invasion under the Invasion Clause of Article I and the Guarantee Clause of Article IV, they surely also qualify as such under the Suspension Clause. And there is significant illegal migration and smuggling of contraband goods going on at virtually all times.

The danger of creating unlimited power to suspend the writ of habeas corpus is exacerbated further if a small “invasion” is enough to trigger the Suspension Clause. If illegal migration and drug smuggling qualify as “invasion” and even a small invasion is sufficient to trigger relevant constitutional provisions, then even small amounts of illegal migration and smuggling would be enough to authorize suspension of the writ.

The Suspension Clause says that even when there is an ongoing “Rebellion or Invasion,” the writ may be suspended only if “the public Safety may require it.” But this is not much of a constraint, as the clause permits suspension even if public safety only “may” require it. Certainty is not necessary. Particularly in border states, including Texas, it is almost always possible to argue that “public safety” may be promoted by suspension. 

The suspension power is not limited to recent immigrants, but applies to U.S. citizens, as well. Historically, suspension has been used against citizens, as was the case during the Civil War. In 2022, 89 percent of people convicted of fentanyl trafficking were U.S. citizens. If illegal migration and drug smuggling qualify as an “invasion” triggering the Suspension Clause, citizens might well be among those detained without charges. Suspension also need not be limited to border states. Undocumented immigrants and drug traffickers can and do make their way to interior states, as well.

British violations of the writ were major grievances of the American colonists before and during the American Revolution. If the original meaning of the Constitution allowed suspension any time illegal migration or cross-border smuggling occurs, that issue would surely have been raised at the Constitutional Convention and in the ratification debates.

The Fifth Circuit or the Supreme Court could, as some other courts have done, hold that the definition of “invasion” is a “political question” that courts are not permitted to resolve. Such a ruling would be dubious. The definition of “invasion” is no more “political” than that of many other words in the Constitution that courts routinely interpret, such as those that determine the relative scope of federal and state power over economic regulation, international trade, and much else. But if judges do rule that the meaning of “invasion” is a political question, they should also hold—as Judge Ezra did in the water buoy and S.B. 4 cases—that such a ruling does not mean Texas can use a declaration of “invasion” as a way to get around federal statutes and empower the state to wage war against foreign nations without congressional authorization.

Legal issues aside, the drumbeat of rhetoric equating drug smuggling and immigration and invasion also has dangerous political implications. An invasion is the kind of thing to which governments usually respond with overwhelming force. The more people assume immigration and drug smuggling are equivalent to an invasion, the greater the likelihood there will be political pressure for such draconian measures as killing migrants, family separation (which Trump may seek to revive if he returns to power), and the idea of invading Mexico to fight the war on drugs more effectively. At the very least, “invasion” rhetoric moves the Overton Window on such proposals in the wrong direction.

Court decisions may not be able to have much impact on these political dynamics. But judicial rejection of Texas’s “invasion” argument can at least forestall the danger of letting border states initiate war anytime they want, and giving the federal government a nearly unlimited power to suspend the writ of habeas corpus.

Ilya Somin is Professor of Law at George Mason University, B. Kenneth Simon Chair in Constitutional Studies at the Cato Institute, and author of Free to Move: Foot Voting, Migration and Political Freedom.

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