The Supreme Court’s decision to uphold the Affordable Care Act’s subsidy scheme is a big win for the law’s proponents and a dramatic rebuff of a challenge that posed the most severe threat to the law since the 2012 challenge to the Constitutionality of the individual mandate.

But today’s victory may have been even more decisive than it looks at first glance.

It isn’t just that the Court ruled six-to-three in favor of the government’s position, with John Roberts and Anthony Kennedy joining the Court’s liberals in support of a single, non-splintered decision, though that’s important.

It’s also that Roberts’ opinion may have precluded any future efforts by a Republican president to use executive discretion to cancel the subsidies for the millions of people on the federal exchange. This option might have been left open if the ruling had been written differently.

The Chief Justice’s opinion tracks with what supporters of the law have been saying for years now. At one point the opinion suggests that the intent of Congress has to be considered in determining the meaning of disputed statutory language. “A fair reading of legislation demands a fair understanding of the legislative plan,” the opinion says. “Congress passed the Affordable Care Act to improve health insurance markets, not to destroy them.”

This tracks with much of the reporting that was done to establish the actual legislative history here (some of which appeared on this blog), and it was an argument rejected angrily by the challengers and their supporters.

But here’s another crucial aspect of the opinion: it ultimately did not base its conclusion on “Chevron deference,” i.e., the idea that Courts should defer to the discretion exercised by an agency (in this case the IRS) when interpreting seemingly confusing or self-contradictory statutes.

Instead, the opinion came down decisively in favor of the government’s reading of the overall law as the right one, says Abbe Gluck, a Yale Law School professor who has written extensively about this case.

The opinion does say the challengers had a strong case based on the isolated text alone — that subsidies go to people on an “exchange established by the state.” The challengers’ “arguments about the plain meaning” of that phrase “are strong,” the opinion says.

But the opinion also says that in “extraordinary cases,” such as this one, it isn’t enough to simply “ask whether the statute is ambiguous, and if so, whether the agency’s interpretation is reasonable.” Instead, the opinion declares that the question at issue — whether the ACA authorizes subsidies to those on federal exchange states — is one of “deep economic and political significance that is central to this statutory scheme.”

The court held that it would not presume that Congress implicitly intended to defer such a central decision to the agency. As such, the Court’s task was to determine the “correct” reading of the disputed phrase.

And the opinion’s answer to that challenge is clear. It states that when the phrase is read in its larger context, the challengers’ reading is “untenable.” It concludes: “the context and structure of the Act compel us to depart from what would otherwise be the most natural reading of the pertinent statutory phrase.”

“Read in context, the Court said it was compelled to read the statute the other way,” Gluck tells me. “That takes the question away from a future administration.”

“A strong six member majority of the court is coalescing around this very clean argument,” Gluck continues.  “That sends a strong signal to people who politically oppose the law that the court understands the law and is not going to tolerate more of this frivolous litigation that tries to destroy the statute by distorting it.”

Republicans today greeted the decision with dismay, vowing to continue the fight. Along these lines, it’s worth pausing to remember that even if this particular challenge was decisively defeated, its fundamental impetus remains very much in force.

“Obamacare is fundamentally broken, increasing health-care costs for millions of Americans,” House Speaker John Boehner (R-Ohio) said Thursday after the Supreme Court’s ruling. (Reuters)

This challenge would not have been possible if so many states — most of them GOP-controlled — had been more willing to participate in bringing the law’s benefits to their own constituents. Though setting up exchanges would theoretically give the states more control over their health care systems, Republicans declined to do so explicitly as part of a broader effort to resist the law wherever possible.

Most GOP leaders still are fundamentally, deeply opposed to the law’s means and methods of moving the country — and the states — towards universal health care. A number of them continue to hold out against the Medicaid expansion, and will likely continue to do so (see the ongoing budget battles in Florida, for example). And that is having a real impact in slowing the law’s success in expanding coverage.

This unrelenting opposition is something that shows no signs of flagging. And this is something that should continue to be a cause of concern for those who support the law and its goals.

This legal challenge was the most potent threat of the moment to the law manifested by that continuing opposition, and as such, its defeat is a tremendous relief. Whether this outcome will dim that underlying opposition is another question entirely, and that matters a great deal, both in terms of the law’s long term prospects and the broader impact it continues to have on our politics in general.