Texas Gov. Greg Abbott’s public declaration of invasion at the Texas-Mexico border is a step in the right direction — for both Texas and the nation.

The governor has rooted his assessment and consequent orders to Texas military and law enforcement in the United States Constitution’s Article I, Section 10. That passage states, in part, that “No State shall … engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.” With this in mind, it’s worth exploring what the Founders meant by “actually invaded,” and what they understood invasion to be.

The invasion clause is among the least invoked Constitutional passages, standing with the Third Amendment prohibition on forced quartering of troops, or the option of the Article V convention because there has been little need for it in the past two centuries.

In part, it is because the United States’ strategic situation has changed tremendously since 1787. Nearly every state expected to face a hostile frontier in 1787, but not after 1920. The federal government, until recently, mostly did its job in protecting American borders. For example, when Mexican depredations threatened American border communities a century back, the Secretary of War called for volunteers in summer 1916 to secure them, keeping garrisons alert and active through 1920. States until recently also had generous latitude to defend themselves and their citizenry. Texas in particular developed a robust record of border self-defense from its statehood in 1845 to about 1920, without resorting to the formal constitutional invocation.

None of these conditions apply in 2022. Four American states, including the two largest — California and Texas — face a hostile southern frontier. The federal government has for years abdicated its responsibility to defend America’s land frontiers; it’s no exaggeration to note that Washington, D.C., devotes more energy and attention to defending Ukraine’s borders than America’s.

Finally, the states have been aggressively excluded from asserting any legitimate interest in their own security and territorial integrity. The wrongly decided 2012 Arizona v. United States erroneously — from a constitutional perspective — forbade states from even a cooperative effort with the federal government in the sphere of border enforcement.

With states forbidden to act, and the federal government refusing to act, we have seen a genuine invasion scenario, as understood by the Founders, emerge. It is important to qualify what this means. The Founders who drafted the Constitution had three major scenarios in mind when conceiving of invasion. One was Indian raids: a clear and present danger in the republic’s first century, and a non-issue now. (Interestingly, the last major example of states engaging in war-making under Article I, Section 10, with federal approval and cooperation, came in just this scenario, with Georgia and Tennessee pursuing the Creek War of 1813-1814.) The second was direct invasion by the armed forces of a foreign state. The third was piracy.

Recognition of invasion was and is a two-step process, which we define as the entry plus enmity test. An invader, to be an invader, must enter a jurisdiction in question — and it must have enmity toward it, overthrowing or curbing legitimate sovereignty within that jurisdiction by either intent or effect. This two-step test has the effect of clarifying who is and is not invading a state: a crucial distinction in both law and practice. A traditional work-seeking economic migrant, for example, is not as an individual an invader: he may have illegally entered the United States (and should therefore be deported), but neither his aim nor his effect is the overthrow or curbing of local, state, or national sovereignty. In other words, he satisfies the test of entry, but not enmity.

The enmity requirement is, on the other hand, amply satisfied by our antagonists on the southern border now. These are not the migrants as such: they are the cartels, criminal syndicates, and their allies in the Mexican state who protect and profit from their work. These elites and their networks have amassed a robust record of not merely entering the United States, but expressing enmity to its sovereignty. When Mexican Army personnel detain a Texas National Guardsman at gunpoint, in Texas, as happened in 2019; when a Texas county sheriff is exposed as a contractor for a Mexican cartel, as happened in 2013; when federal, state, and local law enforcement report seeing weapons trained upon them from the Mexican side of the Rio Grande; when the current president of Mexico more or less openly has a political alliance with the Sinaloan cartel, and de facto shuts down Mexican cooperation with American law enforcement; when Texas families flee homes and communities in which they have deep roots because there is no protection from depredations issuing from Mexico; and when the human-trafficking networks in Mexico have successfully pushed several million trafficked victims across the border in 2022 alone — then we have ample cause to declare the enmity requirement satisfied.

There is a clear and persistent effort to curb American sovereignty by actors whom the Founders would have immediately recognized: a foreign power and its armed forces in the deeply corrupt Mexican state — and piratical actors in Mexican cartels and organized crime.

There is an invasion underway, in the full meaning intended by the Constitution. The federal government is unlikely to do much about it. The Biden administration certainly will not—its DHS leadership under Secretary Mayorkas seems to view American border security strictly through the lens of partisan advantage, and Ambassador to Mexico Ken Salazar is famously friendly with the very same Mexican president who is plunging Mexico into an era of militarized state-narco rule. In the face of this federal dereliction of constitutional duty, Texas Gov. Abbott is setting the stage to assert his own.