Almost immediately, this framework—along with other major pieces of the ACA—faced partisan opposition and legal scrutiny. The most important legal challenge was the NFIB v. Sebelius case that went before the Supreme Court in 2012. In a controversial 5–4 nail-biter, the Court deemed the individual mandate constitutional because it derived from Congress’s ability to levy taxes. Four conservative justices dissented from that decision, arguing that the Court had improperly saved the ACA: The rest of the law wouldn’t have survived if the justices had decided against the mandate, they said, because the nullification would’ve created an “inability of the other major provisions to operate as Congress intended.”

The Texas-led suit has roots in both this decision and the latest congressional challenge to the ACA. Last year, following dozens of failed legislative attempts to repeal the law, the GOP passed its major tax reform, which included a measure to undermine the very individual mandate that had been such a controversial part of the NFIB decision. By law, the bill couldn’t entirely repeal the mandate; instead, it made the tax penalty zero dollars effective in 2019, meaning it will functionally cease to exist after that.

The Texas challenge, initiated in February, reasons as follows: If the individual mandate, per the Court, is only constitutional because it constitutes a tax, and if that tax has effectively been eliminated, then the tax-less mandate that remains on the books is therefore unconstitutional. What’s more, in an echo of the justices’ NFIB dissent, Texas and the other states argue that invalidating the mandate should invalidate the whole ACA, because the law can’t function the way Congress wanted it to without the mandate in place.

Which brings us back to the Justice Department. In its filing this week affirming the main legal premises of the lawsuit, the DOJ reasoned that because it believes the Supreme Court should soon declare the taxless mandate unconstitutional, the preexisting-conditions provisions so closely attached to it should also be nixed.

The Texas-led lawsuit has a long way to go in its arguments. As Jonathan Cohn at HuffPost and Nicholas Bagley in the Incidental Economist health-policy blog note, there’s major disagreement over whether the empty individual mandate is unconstitutional at all. But the debate is even more complicated than that: Even if the mandate were declared unconstitutional, it would be difficult to argue that the decision would render the law’s other major provisions unable to “operate as Congress intended.” The only part of the law that was changed was the mandate; Congress’s intent was clearly to keep the preexisting-conditions ban and other major pieces of the law in place. Thus, those parts of the law would survive the mandate’s unconstitutionality.