The facts underlying Hencely v. Fluor Corporation, a case the Supreme Court handed down on Wednesday, are horrible and tragic.

During a 2016 Veterans Day celebration on Bagram Airfield, a US military base in Afghanistan, a suicide bomber named Ahmad Nayeb detonated an explosion that killed five people and wounded 17 more. One of the wounded was Army Specialist Winston Hencely, who confronted the bomber and attempted to question him — causing Nayeb to set off his suicide vest shortly after Hencely approached him.

The Army believes that Hencely’s actions “likely prevent[ed] a far greater tragedy,” because the soldier stopped Nayeb from triggering the explosion in a location where it could have killed more people. Hencely is now permanently disabled from skull and brain injuries suffered during the bombing.

The legal issue in Hencely involves “preemption,” a constitutional principle dictating that, when federal law and state law are at odds with each other, the federal law prevails and will often displace the state law entirely. After the bombing, Hencely sued Fluor Corporation, a military contractor that employed Nayeb, claiming that Fluor violated South Carolina law by failing to adequately supervise Nayeb. Fluor has two subsidiaries in South Carolina.

In Hencely, six justices concluded that the wounded soldier’s lawsuit is not preempted, and thus does not need to be dismissed before any court determines if Fluor should be liable. While all three of the Court’s Democrats sided with Hencely, the case cleaved the Republican justices straight down the middle (and not in the way that the Republican justices ordinarily split when they split down the middle). Justice Clarence Thomas wrote the majority opinion, which was also joined by Republican Justices Neil Gorsuch and Amy Coney Barrett. Justice Samuel Alito wrote the dissent, joined by Chief Justice John Roberts and Justice Brett Kavanaugh.

The question of when a particular state law is preempted by federal law does not always divide the justices along familiar political lines. An expansive approach to preemption sometimes yields results that liberals will celebrate, and other times, benefits right-leaning policymakers. In Wyeth v. Levine (2009), for example, Thomas also took a narrow view of when federal laws should be read to preempt a state law, and thus ruled against a pharmaceutical company whose drug caused a woman to lose her arm. But advocates for immigrants also frequently argue that state laws targeting their clients are preempted by federal law.

So the Hencely case is significant because it reveals how each of the current justices tends to view preemption cases. Thomas has long questioned many of the Court’s previous cases, taking a broad view of preemption, and it now appears that Gorsuch and Barrett share some of his skepticism. The other three Republicans, by contrast, appear much more sympathetic to arguments that the federal government should have exclusive control over some areas of US policy.

The easiest cases involve “express” presumption, when Congress enacts a law that explicitly invalidates particular kinds of state laws. Imagine, for example, that South Carolina had a law requiring all T-shirts to be made with 100% yellow fabric. If Congress passed a law saying that “no state may regulate the color of T-shirts,” that federal law would expressly preempt South Carolina’s yellow shirt law.

Other relatively easy cases involve “impossibility” preemption, which occurs when it is impossible for someone to simultaneously comply with a state law and a different federal law. If Congress passed a law requiring all T-shirts to be made with 100% red fabric, for example, the hypothetical yellow shirt law would also be preempted because a shirt cannot be entirely red and entirely yellow at the same time.

The hardest preemption cases, meanwhile, involve state laws that may undercut a federal policy or undermine the goals of a federal law, but that do not present such a clear conflict with a federal law that it is impossible to comply with both laws. In Hines v. Davidowitz (1941), for example, the Supreme Court struck down a Pennsylvania law requiring noncitizens to register with the state, even though no federal law explicitly prohibited Pennsylvania from enacting such a registration regime.

The Court reasoned that Congress had passed “a broad and comprehensive plan describing the terms and conditions upon which aliens may enter this country, how they may acquire citizenship, and the manner in which they may be deported,” and that this plan fully established the rights and obligations of noncitizens within the United States. If Pennsylvania were allowed to supplement this federal plan with additional regulation, that would stand “as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress.”

Hencely involved a dispute that more closely resembles Hines than it does the more clear cut hypotheticals involving yellow T-shirts. On the one hand, Nayeb had a job at Bagram because of a US military program called “Afghan First,” which, as Thomas explains in his opinion, “sought to stimulate the local economy and stabilize the Afghan Government by requiring contractors to hire Afghans ‘to the maximum extent possible.’”

Thus, as Alito wrote in dissent, the military had apparently decided that these “long-term foreign policy and defense objectives” justified the risk that an Afghan national might find work on a US military facility, and then use their limited access to that facility in order to commit a terrorist attack.

In other words, much as the Pennsylvania immigrant registration law undercut the federal government’s broader goals of providing a certain level of civil liberties to noncitizens, Alito argued that allowing Hencely to sue a military contractor who complied with the federal government’s policy of giving jobs to Afghan nationals would undermine that policy.

Thomas, meanwhile, concluded that, while Fluor may have hired Nayeb in order to comply with a federal directive, it allegedly did not comply with all of its obligations to the federal government. Though Nayeb was allowed on the base, he was a “red-badge holder” and thus was supposed to be closely monitored and often escorted through the base by Fluor.

An Army report, Thomas writes, concluded that “Fluor’s lax supervision … allowed Nayeb to check out tools that he did not need for his job and that he used to make the bomb inside Bagram.” It also found that Fluor failed to escort Nayeb off the base at the end of his shift.

Ultimately, Thomas disagrees with Alito that a state law can be preempted merely because it undercuts the military’s Afghan First policy in some oblique way. In Thomas’s view, preemption is only justified when “the government has directed a contractor to do the very thing” that is forbidden by state law. Hencely did not sue Fluor for hiring Nayeb; he sued Fluor for failing to adequately supervise Nayeb, and the federal government did, indeed, direct Fluor to monitor and escort red-badge-holding Afghan nationals.

Thomas’s opinion in Hencely won’t surprise anyone familiar with his opinion concurring in the judgment in Wyeth, the case ruling in favor of the woman who lost her arm due to a drug’s side effect. In that case, Thomas wrote that “I have become increasingly skeptical of this Court’s ‘purposes and objectives’ pre-emption jurisprudence,” which allows courts to invalidate “state laws based on perceived conflicts with broad federal policy objectives … that are not embodied within the text of federal law.”

Justice Thomas, in other words, appears to reject cases like Hines, which hold that federal law can sometimes displace state laws even when there isn’t an unavoidable conflict between the two laws. The fact that Gorsuch and Barrett joined his opinion in Hencely suggests that these two relatively new justices, who weren’t on the Court when Wyeth was decided, may share Thomas’s views.

As a practical matter, that’s good news for consumers and for consumer rights lawyers. Cases like Wyeth, where the manufacturer of a potentially dangerous product claims that state lawsuits arising out of that product are preempted by federal law, are fairly common. Hencely suggests that at least three of the Court’s Republicans will not support these preemption claims, at least when federal law does not clearly conflict with a state law.

At the same time, immigrants and immigration advocates will likely look upon Hencely with trepidation, as it suggests that this three-justice bloc may also seek to overrule Hines, a seminal precedent establishing that states typically may not impose restrictions on immigrants that cannot be found in federal law.

Preemption is not an issue that always favors the left or the right. Sometimes a state law benefits traditionally liberal causes, and sometimes it tries to advance a more right-wing goal. But Hencely suggests that the current Court will be more cautious about preemption claims generally, regardless of who benefits from that decision.