New York City Mayor Bill de Blasio apparently missed the memo from FAIR’s Research Director Matt O’Brien. De Blasio seems to think that he, or at least someone, can and should somehow keep particular law enforcement officers—namely Immigration and Customs Enforcement (ICE)—out of public courthouses in his city. And he’s clearly not alone in this kind of dangerous wishful thinking.

In a softball interview on December 15, the mayor said he believes “[t]he court system should be an off-limits place to ICE” and that the city “had no problem” imposing a blanket rule that keeps ICE off the property of its public schools and hospitals, so the courts should be able to do the same thing.

But of course the idea that New York City ever actually imposed any such rule on ICE, or ever could, is nonsense. City officials can issue all the feel-good “guidance” documents they want about immigration enforcement in schools and hospitals, but they still legally mean absolutely nothing, since ICE is a federal agency over which the city has no authority. If de Blasio and Co. don’t understand that, maybe they also missed the Supremacy Clause of the U.S. Constitution, which says that federal law is the supreme law of the land.

One thing federal law absolutely does not say is that ICE’s authority or the arrest powers of its officers end at the door of a school or hospital (or of a courthouse either). The only reason ICE rarely enters or makes arrests at schools, hospitals or houses of worship is because the agency itself has chosen not to, by adopting a policy saying it regards those places as “Sensitive Locations.” The policy isn’t required by law and it doesn’t even rule out entry or enforcement at those places: it just spells out when ICE personnel do and don’t need approval from their supervisors to do so. And the policy certainly isn’t because of rules adopted by New York City or any other local government.

ICE’s Sensitive Locations Policy doesn’t include courthouses. It doesn’t include them for a few very good reasons. First, especially in sanctuary cities like New York where local police refuse to honor detainers to hold illegal aliens for ICE and where local jails grant ICE little or no access, a courthouse is the next best alternative for protecting the safety of ICE’s own officers, the aliens being arrested themselves, and any nearby bystanders. This should be obvious because as ICE spokeswoman Rachael Yong Yow points out, “everyone inside the building has already been screened “for weapons and other contraband.”” This reason alone simply cannot be overstated: when ICE has to make street arrests in the community, of people who may be armed, the potential for violence escalates dramatically.

Second, courthouses may be the only place ICE can actually find particular illegal aliens who they’re already looking for. ICE explains this rationale in its own online Frequently Asked Questions on Sensitive Locations and Courthouse Arrests: “tracking down priority fugitives is highly resource-intensive. It is not uncommon for criminal alien targets to utilize multiple aliases and provide authorities with false addresses. Many do not have a stable place of employment. Absent a viable address for a residence or place of employment, a courthouse may afford the most likely opportunity to locate a target and take him or her into custody.”

Finally, courthouses are by long custom, by principle and by law expected to be open to the entire general public in ways that schools, hospitals and even places of worship are not. They are public places for doing public business openly and in public view. This understanding is enshrined in the guarantee by the Sixth Amendment to the U.S. Constitution that “[i]n all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial,” [emphasis added]but it applies to everything done in a courthouse, which is presumed to be open to all unless a judge finds legal grounds to close or restrict access to an individual case. Indeed, New York’s own rules of court proudly proclaim this very same principle, stating that “[t]he sittings of every court within this state shall be public,” which actually goes beyond the Sixth Amendment to cover not only criminal but civil, family court, and other legal proceedings. And ICE officers are no less members of the public than anyone else is.

In New York, unlike most states, those rules of court are laws enacted by the state legislature. So Mayor de Blasio has no direct control over them. But let’s assume for a moment he could convince the legislature to pass a law saying the courts are open to the public “except for ICE,” and then get Governor Andrew Cuomo to sign it. In New York such a scenario unfortunately doesn’t sound like all that much of a stretch. So then ICE could be kept out of New York courthouses…right?

Wrong, because then that would be the state as well the city having missed the Supremacy Clause (again). No matter what state law might say—or be changed to say in the future—federal law is still the supreme law of the land. And one thing federal law absolutely does say is that interfering with immigration enforcement is a felony. Or rather, potentially one or more of several felonies: not just “conceal[ing], harbor[ing], or shield[ing]” illegal aliens, but also Obstruction of Justice. Notably, there are no exceptions for local elected officials, judges, police, or anyone else.

So ultimately, if Bill de Blasio or any other sanctuary-city politicians around the country want to risk federal prison by blocking the courthouse door to ICE, they’re welcome to try.