The Supreme Court on Tuesday is taking up a case that presents a critical question of law: Can a U.S. law enforcement officer be sued in American courts for the death of a foreigner outside the United States?

For most of American history, the answer to that question has been a clear and emphatic “no.” Courts for two centuries have held that constitutional rights do not apply to foreigners with no voluntary connection to the United States.

“That has been under a lot of pressure and challenge recently.”

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That the high court even agreed to take Hernández v. Mesa casts doubt on that long-held understanding of the law, however.

“That has been under a lot of pressure and challenge recently,” Fordham University School of Law professor Andrew Kent told reporters on a conference call last week.

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The Supreme Court opened the door to a possible revision with a 2008 ruling that held that prisoners at the Guantanamo Bay, Cuba, detention facility had a right to petition the U.S. courts even though Gitmo is on foreign soil and the detainees were foreigners who never even had been to the United States.

Attorneys for the family of Sergio Hernández quote liberally from that case, Boumediene v. Bush, in their written legal arguments.

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U.S. Border Patrol agents worry a decision in favor of the plaintiffs would make it harder for them to do their jobs, and legal scholars speculate that it could — depending on how expansive the language in the opinion is — impact immigration more generally.

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The facts of the case are unusual — and in dispute. The plaintiffs contend that Hernández, who was 15 at the time in 2010, was playing a game with some friends that involved running up to a fence at the top of an embankment in front of a culvert that separates Mexico from the United States between El Paso, Texas, and Ciudad Juárez.

A Rock-Throwing Smuggler

Attorneys for the Border Patrol officer, Jesus Mesa Jr., allege that Hernández was a smuggler who twice had been arrested in the United States but allowed to return to Mexico because of his age.

While Mesa was detaining one of the youths, according to defense lawyers, Hernández ran back to the Mexican side of the border and hurled rocks at him. What is not in dispute is that Mesa fired across the border, killing Hernández.

The District Court judge dismissed the ensuing lawsuit, and the 5th U.S. Circuit Court of Appeals in New Orleans upheld the decision. Attorneys for the Hernández family argue that the case is similar to the situation in Boumediene. Like Gitmo, they argue, border officers exercise a level of control along the border that makes it effectively U.S. territory.

“If this Court were to side with the government, it would effectively turn the border into an on-off switch for fundamental constitutional protection,” they write in a court filing.

But Mesa’s attorneys argue that the border is not at all like the U.S. military base in Cuba. The dividing line between Mexico and the United States is fixed, they write.

“To hold otherwise would create extraterritorial jurisdictional jurisprudence based on subjective determinations on where to draw the line,” the brief states.

Both the defense attorneys and lawyers for the federal government cite a 1990 case, United States v. Verdugo-Urquidez, in which the high court ruled that the Fourth Amendment did not cover an accused Mexican drug dealer. In that case, Rene Martin Verdugo-Urquidez was in jail in the United States when Drug Enforcement Administration got permission from the Mexican government to search his home.

The court rejected the defendant’s challenge that his Fourth Amendment rights had been violated since DEA agents did not obtain a warrant.

Government lawyers ague in the Hernández v. Mesa case that the courts should defer to Congress about what rights foreigners have.

“The need for caution is reinforced by the fact that, in a variety of statutes, Congress has long taken care not to provide aliens injured abroad with the sort of judicial damages remedy petitioners seek,” the brief states.

Border Patrol Agents Watching

The government also agues that even if the Hernández did enjoy constitutional protections, Mesa is entitled to immunity because he was acting in his official capacity as a law enforcement officer.

Brandon Judd, president of the National Border Patrol Council, expressed confidence that Mesa will prevail. He praised the appellate court ruling.

“It seems pretty straightforward and pretty sound,” he said. “It’s the right decision. I don’t see how agents … could be held civilly liable for something that didn’t happen in our country.”

Upholding the lower court decision would “let our officers know they can continue to our jobs without fear of reprisal,” Judd added.

With the court currently divided 4-4 between more liberal and more conservative justices, a split decision would leave the appellate decision in effect. But Kent, the Fordham professor, noted that Kennedy wrote the majority opinion in the Guantanamo case. If he decides that precedent applies more broadly, a five-vote majority to overturn the lower court decision is possible.

A narrowly tailed opinion could limit the impact.

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“That hasn’t been, in the past, how Justice Kennedy has done business,” Kent said, noting that the justice’s majority opinion in the Guantanamo case was open-ended.

Such an outcome in this case could open the door to further challenges, he said. Judicial second-guessing of the government’s decisions affecting foreigners is an issue in the legal battle over President Donald Trump’s travel ban. Kent said it also potentially could impact surveillance of foreigners by U.S. intelligence services.

“They could be pretty significant,” he said. “Justice Kennedy, as you probably know, sort of favors often kind of flowery, loose language. He’s a big believer in sort of the power of the federal courts decide any and all questions that come before it. And he tends to talk about these issue of where the Constitution applies in pretty vague ways that don’t give a lot of direction to executive branch in particular.”