While the nurse quarantined in New Jersey has been released, the ACLU continues to push back against such measures by the states, and as the disease spreads, these questions will persist.

Yesterday I discussed potential due process challenges to Ebola quarantines. Another possible constitutional objection to such measures, as Josh Blackman points out, is preemption because of a conflict with federal policy. The issue is not that state quarantine rules are tougher than the CDC suggests – federal law explicitly allows states to be tougher in this regard. Rather, it is that the quarantine of health care workers returning from West Africa conflicts with the Obama Administration’s policy of not discouraging them from going to the hot zone, as evidenced by the decision to not bar air traffic from the area.

As it happens, the Supreme Court’s discussions of the permissibility of quarantines has been mostly in the preemption contexts, going back to the landmark dormant commerce clause case, Gibbons v. Ogden in 1824. (A quarantine is by definition a prophylactic measure that applies to those who are not necessarily sick of infected.) The Court has ruled strongly against any kind of implied preemption for quarantines. Rather, it has said that unless the federal government adopts quarantine laws or regulations inconsistent with those of the states, “the laws of the state on the subject are [presumptively] valid.”

This means that the Executive could issue regulations preempting the New Jersey quarantine, but critical statements at press conferences do not have this effect.

Quarantines have traditionally been administered by states, and applied first and foremost at ports of entry. Thus the people and vessels subject to quarantine were those that the U.S. had a policy of admitting – otherwise they would not there in the first place and there would be nothing to quarantine. Yet such quarantines were never understood to conflict with federal commerce or immigration policy; rather, federal policy is premised on states applying their police powers, as the Court ruled in Compagnie Francaise de Navigation a Vapeur v. Louisiana. Indeed, in that case the “quarantine” that was upheld was clearly a pretext for excluding Italian immigrants.

I think Prof. Blackman would not dispute any of this. Rather, he suggests that if the reasoning of Arizona v. United States, the recent immigration preemption case, were taken (too) broadly, it could undo two centuries of quarantine preemption jurisprudence. However, Arizona can read more narrowly.

In Arizona, both the state and federal laws in question dealt with the same thing: illegal immigrants, and the sanctions against them. The state law was tougher than the federal one. Here the federal policy deals with one thing – international air travel – while the state rules deal with something different, the movement of persons within the state who may have been exposed. As it happens, they may have arrived through air travel.

One would not think taxes a state places on airport taxis or other airport rules would be preempted by a federal policy to allow people to travel to West Africa, even if they raise the cost of such travel. Rather, this is the assumed background against which the federal policy operates. Similarly, the application of general state powers to ensure the health of the population are not going beyond the federal law, but are rather the assumed background on which the latter acts.

Just as Blackman uses the quarantine to implicitly criticize Arizona, and particularly the government’s arguments there, Michael Dorf uses the quarantine issue to cast a bad light on narrow readings of the Commerce Clause by conservative justices, in particular, by comparing the spread of Ebola to the danger posed by mentally ill people, or guns near schools.

I find the analogy inapt. Contagious viruses by definition do actually travel across jurisdictional lines, even without their vector doing so. Violent mental illness, by contrast, is not catching: the person is only a threat to those around him. Guns in school zones by definition do not cross state lines.

Addendum: One of the Supreme Court cases mentioned above, Morgan’s Louisiana, has this memorable observation: “If there is a city in the United States which has need of qurantine laws it is New Orleans.”