In 1993, Congress passed the Brady Handgun Violence Prevention Act. Among its various initiatives, it provided for the creation of a national background check system by which to screen prospective gun purchasers. This created a dilemma, however: the United States is a mess of separate and overlapping jurisdictions, and most crime is dealt with at the state and local level. There is no centralized police force with comprehensive records, so a centralized database takes time to generate. What to do in the interim?

A solution was struck upon: make the sheriffs do it. Until the federal system could get up and running, firearms dealers would submit background check information to local law enforcement. These local law enforcement officers would make their best efforts, given whatever data was practically at hand, to determine if there was a reason the person in question was not eligible to buy a gun.

Sheriff Jay Printz of Ravalli County, Montana, being the sort of person who gets elected Sheriff of Ravalli Country, Montana, was not pleased with this expansion of his job description. He brought suit, and in 1997 the Supreme Court held that, whatever else the federal government may do, it is not within its power to commandeer local law enforcement to do its job for it. If the federal government wants something done, it can very well do it itself (or alternatively offer money to encourage voluntary assistance).

In the blinkered way we analyze constitutional law, Printz goes in pile of “conservative” decisions. Conservatives like federalism. They like it so much, it’s the one time they cite Justice Brandeis with approval — his description of states as “laboratories of democracy” induces conservative tumescence.

What Brandeis neglected to mention is that, sometimes, laboratories explode. And then it turns out conservatives lose their vigor.

Or rather it turns out that not all the laboratories are staffed with conservatives. Such is the case with what are now termed “sanctuary cities.” Different cities may have different approaches, but the platonic form is that a city government, exercising its experimental prerogatives, instructs its police officers not to bother with violations of federal immigration law. Instead they investigate murders and hand out traffic tickets and all the other sundry tasks we are familiar with. If they detain a suspect in the course of their shift, or interview a person around the neighborhood, they don’t enquire as to his immigration status. If they happen to divine that the person is not present in the country legally, they don’t bother about it — it’s not within their job description. If a federal immigration official tracks down a boarder-jumper (or, as is becoming more likely these days, a visa-overstayer), the local police decline to assist, and just let our federal official go about his day.

There are permutations of this that might prove troubling, where local officials actively obstruct federal officers in the performance of their duties, but by in large that is not what we’re talking about. Recall that the Supreme Court held (over some compelling dissents), that aggressive enforcement of federal immigration law by local police itself is a violation of federal prerogatives. Immigration law is a federal concern, and for good reason.

And thus we have the revenge of Printz. Republican politicians have declared these municipalities enemies of the state. The current President has attempted to banish sanctuary cities into outlawry. As George Will points out, the President’s Executive Order on this matter “is either a superfluous nullity or it is constitutional vandalism.” The order purports to deny federal funds to those who do not comply sufficiently with the President’s whims. The ultimate way in which the courts will apply the mushy contours of the conditional spending doctrine would require training in Sovietology beyond that of your humble correspondent. But suffice it to say, as Mr. Will suggests, that to the extent the conservatives try and demand fealty to their immigration crusade by becoming punitive, they will discover that they hate even the portion of Chief Justice Roberts’ NFIB decision they thought they liked, and to the extent the Oval Office demands simply that local officials not engage in obstruction they are largely fighting with their own shadow.

Legal rules work best when goose and gander are both well sauced. And in federalism, as in sports, no one likes the guy who shows up to the fair weather of a playoff game decked out in team regalia, and then asks what the players’ names are.