In its decision Wednesday striking down the Affordable Care Act's individual mandate, the U.S. Court of Appeals for the Fifth Circuit expressed no opinion on whether a Texas trial judge, once the case returns to him, should sever the provision to save the rest of the landmark health care law.

The appeals court could have declared the entirety of Obamacare unlawful, but instead punted to the trial judge for further review. Central to that fresh look, now, is whether the whole law must fall because one part is allegedly unlawful. The divided Fifth Circuit panel at various times pointed to the concerns Justice Clarence Thomas has articulated about the power of courts to strike one thing in a law in order to keep the whole intact.

Still, whether the district court, which originally struck down the entire law, actually will get a second shot at the question of severability is not clear. Democratic-led supporters of Obamacare, including California Attorney General Xavier Becerra, have vowed to press an appeal in the U.S. Supreme Court. Such a move in the coming weeks could force the court to act swiftly, perhaps even agreeing to hear a challenge this term.

"The Supreme Court might choose to hear the case, Texas v. United States, right away, setting up a constitutional showdown that could become the centerpiece of the 2020 presidential election," law professor Nicholas Bagley wrote in a piece at The Atlantic on Thursday. "Or the justices could wait until the lower court rules, leaving the fate of Obamacare in limbo for years."

In any scenario, the Supreme Court's "severability doctrine" will play a central role as the case plays out. The doctrine holds that when a law is partially unconstitutional, the Supreme Court must save its valid parts unless lawmakers would not have intended those parts to remain in effect absent the unconstitutional provisions.

Less than two years ago, Thomas dropped into an opinion one of his regular "time to reconsider or overrule" precedents or doctrines—this time in the case Murphy v. National Collegiate Athletic Association.

The high court decision, written by Justice Samuel Alito Jr., struck down the entire 1992 Professional and Amateur Sports Protection Act, which prohibited states from authorizing sports gambling. Thomas, writing only for himself, said the majority opinion gave the best answer to this question: Would Congress still have passed the valid sections of the law had it known about the constitutional invalidity of the other portions of the statute?

"In a future case," Thomas said, "we should take another look at our severability precedents." Thomas said the severability doctrine appears to be "in tension with traditional limits on judicial authority."

The Fifth Circuit's Obamacare decision at various parts quoted Thomas's skepticism of the severability doctrine.

Thomas' concurring opinion in the sports-gambling case, the appeals court said, provides "two reasons why navigating between the Scylla of poking small but critical holes in complex, carefully crafted legislative bargains and the Charybdis of invalidating more duly enacted legislation than necessary stands 'in tension with traditional limits on judicial authority.'"

In the gambling case, Thomas said at one point that the severability doctrine requires judges to determine what Congress would have intended had it known that part of its statute was unconstitutional. But it seems unlikely that the enacting Congress had any intent on this question; Congress typically does not pass statutes with the expectation that some part will later be deemed unconstitutional."

No other justice joined Thomas in his statements about the severability doctrine. Three justices—Ruth Bader Ginsburg, Stephen Breyer and Sonia Sotomayor—would have applied the doctrine to save the remainder of the sports betting law.

Ginsburg's dissenting opinion accused the majority of wielding an "ax" instead of a "scalpel"  to the law. "When a statute reveals a constitutional flaw, the Court ordinarily engages in a salvage rather than a demolition operation," she wrote.

In the first Supreme Court challenge to the Affordable Care Act in 2012, Thomas and three other justices rejected applying the severability doctrine after the majority struck down the Medicaid expansion section of the law requiring states to participate in order to get funds. Because they viewed the individual mandate and the Medicaid expansion as unconstitutional and integral to the functioning of the law, they said the entire law was invalid.

Only two of those four justices remain on the bench—Thomas and Alito. Justice Antonin Scalia died in 2016, and Justice Anthony Kennedy retired in 2018.

Whether Thomas could find a majority for his view of severability if the latest Obamacare case returns to the Supreme Court is hard to predict.

Justice Neil Gorsuch, who succeeded Scalia, may be sympathetic to Thomas' view of the importance of adhering to the text of a law without inquiring into what lawmakers were thinking at the time.

Kavanaugh Brett Kavanaugh was nominated Monday to the U.S. Supreme Court at a ceremony in the East Room. Photo: Diego M. Radzinschi /NLJ

Kavanaugh has written critically about the severability doctrine. In a 2016 Harvard Law Review article, he described the doctrine as a "mess," and he called inquiries into congressional intent an "inherently suspect exercise."

The Trump administration's U.S. Justice Department initially argued that the individual mandate could be erased from the health law while keeping it otherwise in place. Main Justice later went further and has now fully embraced the Texas court's declaration that the entire Affordable Care Act must be struck down.

"Instead of rewriting the statute by picking and choosing which provisions to invalidate, the proper course is to strike it down in its entirety," the Justice Department asserted in a brief in the Fifth Circuit.

Legal scholars have criticized the Justice Department's arguments on severability, noting that Congress, although it repealed the individual mandate, did not otherwise scrap the entire Affordable Care Act. "Congress repealed the mandate because it thought it was bad policy and left the rest of the ACA standing. That's all it did, and that's all it should be taken to have done," Bagley, the law professor, said in a post last year.

Judge Carolyn Dineen King of the U.S. Court of Appeals for the Fifth Circuit, writing in dissent in Wednesday's Obamacare decision, said the Texas trial judge had "no reason" to conclude "any provision of the ACA was inseverable from the coverage requirement." She accused her colleagues—Judges Jennifer Elrod and Kurt Engelhardt—of perpetuating the "judicial overreach" of the trial court.

"The legitimacy of the judicial branch as a countermajoritarian institution in an otherwise democratic system depends on its ability to operate with restraint—and especially so in a high-profile case such as the one at bar," King wrote.