Does Mass Illegal Entry Count as an Invasion Under the Constitution

Few words in the Constitution are asked to carry as much weight as "invasion." Say it at a dinner table and you will hear one person insist it is the only honest description of what happens at the southern border, and another insist that it is an outrage to use a soldier's word for a mother with a child. Both are sure. Neither has usually read the clauses.

I want to do the reading, because the clauses are real, the question is serious, and conservatives themselves are split. Some of the most careful constitutional thinkers on our side think the word reaches organized, hostile migration. Others think it does not. A fair hearing for both readings has to come before any verdict, so that is the order I will follow: the text, the founding-era meaning, the court decisions, the limits on any state's claim, and then the position I think is strongest.

The Two Clauses

The word appears twice in the Constitution's operative text. The first is Article IV, Section 4, which reads:

The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.

Notice who has the duty here. The United States, meaning the national government, "shall protect each of them against Invasion." It is a promise from the whole nation to each state. It is also a promise that does not wait for the state to ask: the "on Application" requirement is attached only to domestic violence, not to invasion.

The second is in Article I, Section 10, Clause 3, in the list of things the states may not do without the consent of Congress. The state may not "keep Troops, or Ships of War in time of Peace," or "engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay." This is a restriction on the states with a safety valve. A state that is actually invaded does not have to wait for permission from Washington to defend itself.

The pairing is important. One clause assigns the national government a duty. The other recognizes a state's emergency right to act when the national government has not or cannot. If "invasion" in these clauses covers unlawful mass migration, then Washington has a constitutional duty to stop it, and a state facing it may in the last extremity defend itself.

What "Invasion" Meant in 1787

The word's meaning is where the whole dispute begins, and here are the facts as I understand them.

In the language of the eighteenth century, an invasion was a hostile entry: an armed incursion by an enemy into a country's territory. Founding-era dictionaries, as I read them, define it as a hostile entrance upon the rights or possessions of another. The paradigm case was an army crossing a border. The Founders had in mind the British, the French, the Spanish, the Indian confederacies, and the pirates and privateers of the age.

James Madison discussed the guarantee clause in Federalist No. 43. He wrote that a protection against invasion is due from every society to the parts composing it. He then explained why the national government needed the power: the states are joined in a union, and an attack on one is an attack on the whole. The context is the military defense of a confederation. Nothing in that essay speaks of civilian migration.

That is the strongest piece of evidence for the narrow reading. If invasion meant armed attack by a hostile force in 1787, then the clauses were written for armies, and we should be careful before stretching them.

The Case for the Broad Reading

Now the other side's best argument, stated as its defenders would state it.

One. The dictionary definition does not require uniforms or cannon. A hostile entrance upon the possessions of another is the heart of the word, and a large, organized and unlawful entrance can be hostile in effect without being a state's army.

Two. The Founders were practical men writing for a future they could not foresee. They worded the clause to protect the states against the threat of foreign attack in whatever form it came, and they could not have known the forms. A clause meant to secure the states should be read to secure them.

Three. Where the entry is organized by criminal enterprises that control territory, move people for profit, smuggle weapons and drugs and exert something like authority over stretches of the border, the picture looks less like individual migration and more like a hostile force with its own command structure. A state facing that has a stronger claim that the clause applies.

Four. If the clause is read so narrowly that a state may never invoke it, then a state faced with a genuine emergency and a federal government that will not act has no recourse, which seems the opposite of what a guarantee is for.

Justice Antonin Scalia leaned this way in his partial dissent in Arizona v. United States (2012). He argued that sovereign states have always had the power to exclude people from their territory, that the Constitution speaks of states protecting themselves when "actually invaded," and that Arizona had not surrendered that power. The majority did not adopt his view, and he wrote it as a dissent, but it came from a careful originalist and it shows that the broad reading has serious support.

The Case for the Narrow Reading

The narrow reading answers in order.

One. The clause's own structure points to military force. It speaks of "Invasion" alongside "domestic Violence," and in Article I, Section 10 it speaks of being "actually invaded" in the same sentence as "War." The company a word keeps tells you its meaning. These are all words of armed conflict.

Two. The Constitution uses other words for the movement of people across the border. It gives Congress the power over naturalization, and it discusses "the Migration or Importation of such Persons as any of the States now existing shall think proper to admit" in Article I, Section 9. If the Founders thought migration was an invasion, they had the vocabulary to say so, and they did not. They knew the difference between a migrant and a soldier.

Three. The Constitution's design puts the power over entry and exclusion in Congress, and the "invasion" clause in the hands of the national government. A reading that lets a state declare an invasion and act on its own would take a power the document gave to Washington and give it to Austin, which would unsettle the structure the clause protects.

Four. The danger of a broad reading is that it has no stopping point. If a large number of unlawful crossings is an invasion, how large? Who decides? A word that can be stretched to cover any inconvenient flow of people can be stretched to cover almost anything, and the Founders were careful about not handing out emergency powers on loose definitions. I count that the strongest of the four points.

What the Courts Have Said

Federal courts have addressed the argument several times, and they have mostly refused to decide it.

In Padavan v. United States (1996), the Second Circuit heard a challenge that the federal government's failure to control illegal immigration violated the guarantee against invasion. The court held that the Invasion Clause challenge presented a political question best left to the political branches. It went further and said that the clause's protection reaches armed hostility from another political entity, which is not the influx of people crossing without permission.

In California v. United States (1997), the Ninth Circuit considered California's claim that the state was being invaded by illegal entry and that the federal government was failing to protect it. The court rejected the claim. It reasoned that the guarantee clause, including the invasion provision, presents political questions that the courts will not resolve, in part because there are no manageable standards for saying when an influx of illegal immigrants becomes an invasion. Other circuits, including the Third Circuit in New Jersey v. United States (1996), reached similar results in similar suits brought by states in the 1990s.

These decisions are worth noting for what they hold and what they do not. They hold that a state cannot sue the federal government in court to force it to treat illegal immigration as an invasion. Their political-question holdings do not forbid the political branches from reading the word broadly, and they do not decide whether a state facing an actual armed incursion could act on its own under Article I, Section 10.

A critic can fairly say that treating the whole question as political leaves states with a guarantee that no court will enforce. A defender of the courts can answer that the Constitution assigns the duty to the political branches, and that voters, not judges, are meant to hold them to it.

The Limits Any State Claim Faces

Suppose you accept the broad reading. A state that wants to act on it still faces four obstacles.

First, the Supremacy Clause. Federal law on immigration is supreme, and Arizona v. United States held that the federal scheme preempted several state attempts to enforce on their own. A state cannot simply replace federal rules with its own.

Second, the textual structure of Article I, Section 10. The "actually invaded" language is a defense against the clause's ban on state war-making, and it tells a state it may act without waiting when "in such imminent Danger as will not admit of delay." It does not hand states a general immigration power. A state acting under it would bear the burden of showing real, present and urgent danger, not a chronic condition.

Third, the political-question decisions. As the circuits have held, a state may not get a federal judge to order the federal government to act. A state that acts on its own will find a court asking whether that act is lawful, and the court may look hard at the claim of invasion.

Fourth, the people involved. The great majority of those crossing are not soldiers, and whatever the word means in a constitutional sense, the state's responses, such as detention and force, are bounded by the Fourteenth Amendment and by ordinary rules about the treatment of persons. A power that is lawfully claimed can still be unlawfully used.

Where I Come Down

Here is my position, offered as an argument, not a dogma.

One. The text and the founding-era meaning make the narrow reading the stronger default. "Invasion" is a word of armed hostility, and the Founders had separate words and separate clauses for migration.

Two. The narrow reading does not strip the clause of meaning in the border context. Where organized criminal groups use armed force, control territory and direct the movement of people as an instrument of hostile enterprise, the facts come closer to the word's core, and the federal government's duty under Article IV, Section 4 is in play. Congress and the president can and should treat that as the serious matter it is, and the way those organizations operate is laid out in The Cartels Run Like Multinational Firms, So Policy Should Treat Them That Way. That is where the broad reading has its best case.

Three. The ordinary case of a family or a worker crossing unlawfully is a violation of law, and it is a serious one, but I do not think it is an invasion in the constitutional sense. Calling it that lets critics change the subject from the law that is being broken to the word we used to describe it.

Four. The remedy is the one the Constitution provides, not a shortcut around it. Congress holds the power over naturalization, appropriations, and the rules of entry. The president holds the duty to enforce. Voters hold both accountable. If the federal government will not enforce the laws on the books, the conservative answer is to elect people who will and to pass laws that work. For the underlying power, see The Chinese Exclusion Case and How the Court Found a Sovereign Power to Exclude. For the struggle over who controls what, see Federalism Lets Fifty States Experiment, and the Constitution Planned It.

Five. I hold this view loosely, and I respect the conservatives who read the word more broadly. They are working with the same text, and the dictionary supports them in part. The honest way to disagree is to read the clauses, which is exactly what too few people do.

The case in brief

1. Article IV, Section 4 makes the United States responsible for protecting each state "against Invasion," and Article I, Section 10 lets a state act if "actually invaded."
2. In founding-era usage, invasion meant hostile armed entry, and Federalist No. 43 treats the guarantee as a matter of the military defense of the union.
3. Conservatives split: the broad reading stresses a hostile entrance in effect, including organized cartel activity, while the narrow reading stresses the clauses' company with war and violence and the Constitution's separate treatment of migration.
4. Federal courts in Padavan (1996) and California v. United States (1997) treated the invasion guarantee as a political question, and Padavan added that invasion means armed hostility from another political entity, not unlawful immigration.
5. The strongest course is the constitutional one: Congress writes the law, the president enforces it, and voters hold both to account.

What you can do: read Article IV, Section 4 and Article I, Section 10, Clause 3 on the Constitution page and then write to your state legislators and your member of Congress asking which reading they hold and why.