The Tenth Amendment to the U.S. Constitution restates a basic rule of American federalism: “The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”

It follows that beyond some boundary, the federal government can’t interfere with state governments’ abilities to exercise state-governmental powers. Otherwise, those words would be an empty promise. But where that boundary sits is not immediately obvious from the text alone.

Beginning in the 1990s, Supreme Court majorities, composed mostly of conservatives, sketched out a boundary that binds lower courts today: Apart from some discrete exceptions, the federal government cannot “commandeer” state governments’ powers to make and carry out laws. Congress could not force states to regulate nuclear waste disposal in a certain way, because this would intrude on the states’ regulatory powers. Congress could not mandate that local law enforcement officials administer federally mandated background checks for gun purchasers. And, per a more recent decision, Congress could not ban states from authorizing sports gambling through state law.

Why draw the line so strictly? In the late twentieth century, different justices on the Court duked it out over the original meaning of the Tenth Amendment, wielding different Federalist Papers to argue about whether the Founders had permitted Congress to use state governments to administer federal law. The stricter anti-commandeering view won out — but originalist justices like Antonin Scalia and Samuel Alito have also invoked some more practical reasons to have the doctrine.

One reason is that if there are two different levels of government with fully distinct powers and incentives, it will be harder, the thinking goes, for either one of them to encroach on individual liberty. A second is political accountability: The legitimacy of a state or local government is rooted in its voters, who should be able to identify, in Alito’s words, “who to credit or blame” for, say, federal background-check enforcement or immigration agencies’ actions. And a third reason is budgetary. If Congress could direct states and localities to carry out federal laws, it could avoid using federal money and leave states holding the bag. Scalia and Alito have emphasized, though, that the constitutional harm of commandeering exists regardless of whether it puts meaningful financial strain on states.

Anyone familiar with the Civil Rights Era can recognize when the language of states’ rights is being used as packaging for reactionary political goals. If a conservative believes the federal government should be less effective at regulating something, one easy way to do so is to get rid of its ability to count on states’ and localities’ help in carrying out the regulatory scheme. 

And anyone familiar with the Republican Party’s electoral record in the late twentieth century could understand why this doctrine might hold political appeal for the conservative coalition: Democrats controlled the House of Representatives continuously from the mid-fifties to the mid-nineties.

But in recent years, the anti-commandeering doctrine — again, previously used to the benefit of gun purchasers, state governments unconcerned with their low-income residents’ health, and the sports-betting industry — has empowered progressive states and localities to withhold their resources and personnel from federal agencies that would otherwise use them in the name of mass deportations. In Washington, for example, state laws limit state and local agency personnel from choosing to assist the feds with immigration enforcement. And now, Seattle (legally a creature of the state) has said its land cannot be commandeered, either.

The subset of small-government advocates who also believe in immigrants’ rights get to say “I told you so” here when it comes to the policy arguments for anti-commandeering. The separation of powers between the state and federal government means the Trump administration can’t necessarily harness the powerful tools of state and local law enforcement to intimidate and deport. The fact that, for instance, the Seattle Police Department is prevented from assisting in federal immigration enforcement means that voters theoretically have the clarity needed to hold those in power who support ICE brutality responsible — it’s the feds. Even budgetary considerations could matter. Despite the firehose of federal money that Republicans in power have directed at ICE and CBP, the agency still faces real resource and personnel constraints that states and localities need not alleviate.

Constitutionalism operates not just through literal law, but as rhetoric. Consider the immense amount of political power that can be rallied behind the invocation of First Amendment freedoms, or the Second Amendment’s language, “shall not be infringed.” Each time a judge or attorney invokes the anti-commandeering doctrine by name, they gesture at the force that underlies any government’s power. Indeed, the word “commandeering” makes me, at least, imagine something like high-seas piracy, where the federal government pulls up alongside a state or local government, hijacks its property, and starts ordering its personnel around at gunpoint.