Readers of this column may recall my expression of shock back in November when the court agreed to hear King v. Burwell. A three-judge panel of the federal appeals court in Richmond, Va., had unanimously rejected the challenge to the law, and the plaintiffs’ appeal didn’t meet the normal criteria for Supreme Court review. A defeat for the government — for the public at large, in my opinion — seemed all but inevitable.

While I’m still plenty disturbed by the court’s action, I’m disturbed as well by the defeatism that pervades the progressive community. To people who care about this case and who want the Affordable Care Act to survive, I have a bit of advice: Before you give up, read the briefs. (Most, although not all, are available on the website of the American Bar Association. ) Having read them this week, I’m beginning to think for the first time that the government may actually prevail.

The challengers have submitted a bunch of me-too arguments from the usual ideological suspects that offer various versions of the narrative concocted to validate the acontextual reading of the law that eliminates subsidies on the federal exchanges. That narrative depicts a highly implausible scenario in which the states — which under the Constitution couldn’t actually be compelled to set up their own exchanges — were given a powerful incentive: Set up your exchange or, if you exercise your choice to default to the feds, your citizens will lose their right to the tax subsidies that will enable them to afford insurance.

The problem for the challengers is that the statute itself nowhere says that, and no one in a position of power appears to have believed at the time that the law would do any such thing. In recent weeks, supporters of the law have had a great deal of fun digging up old statements and video clips demonstrating the contemporaneous belief of prominent Republicans that the subsidies would be available to everyone. The website Talking Points Memo posted one such revelation the other day about Representative Paul Ryan, who at the time was the ranking Republican on the House Budget Committee.

Beyond what various people hoped or expected, there is a deeper issue that the challengers ignore but on which the government’s briefs are utterly persuasive. A fascinating brief filed in support of the government by an unusual coalition of 23 red-state and blue-state attorneys general (some from states with their own exchanges and others from federal-exchange states) maintains that the challengers’ narrative would “violate basic principles of cooperative federalism by surprising the states with a dramatic hidden consequence of their exchange election.”

This brief, written in the Virginia attorney general’s office, continues: “Every state engaged in extensive deliberations to select the exchange best suited to its needs. None had reason to believe that choosing a federally facilitated exchange would alter so fundamental a feature of the A.C.A. as the availability of tax credits. Nothing in the A.C.A. provided clear notice of that risk, and retroactively imposing such a new condition now would upend the bargain the states thought they had struck.”

There are abundant Supreme Court precedents that require Congress to give states “clear notice” of the consequences of the choices a federal law invites them to make. Justice Samuel A. Alito Jr. invoked that principle in a 2006 case interpreting the Individuals With Disabilities Education Act, a case cited by the 23 attorneys general. The government’s own brief, filed by Solicitor General Donald B. Verrilli Jr., observes that “it would be astonishing if Congress had buried a critically important statewide bar to the subsidies under this landmark legislation” in technical sub-clauses.