The reason, they say, is that those 34 states declined to establish their own marketplaces, and relied instead on the federal government to do so. One section of the law says that subsidies go to customers of exchanges "established by the state."
That was not the intention of the members of Congress who wrote and passed the Affordable Care Act, or of President Barack Obama who signed it into law. To the contrary, the mandate that Americans purchase insurance and subsidies for those with modest incomes are the fundamental mechanisms that allow Obamacare to work.
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Congressional Budget Office analyses of the law before its passage never considered the possibility that some Americans would be ineligible for subsidies if their states relied on federal marketplaces. The law as a whole, the Obama administration argues, makes that clear.
In an era in which political parties were less ideologically polarized, a case like this might never have reached the Supreme Court. If it did, the potential solution would be simple enough—Congress could pass a fix making the disputed passage consistent with the rest of the law as intended by its authors.
But today's Congress is so polarized and gridlocked that such a simple fix is no longer possible. Which means a victory by the plaintiffs—not implausible in a court with a conservative majority—could leave millions of Americans without the subsidies they expected when they signed up.
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Republican opponents of the law say they won't leave those Americans to fend for themselves; Instead, they would pass some yet-undefined alternative to Obamacare. "We're not going to sit back and do nothing," Senate Finance Chairman Orrin Hatch told me.
But disagreements within the Republican Party, between the House and Senate, and between Republicans and Democrats render the odds of passage for any new health legislation very long.
Obama administration officials say they have no backup plan for a Supreme Court defeat. That's their attempt to increase pressure on justices by underscoring the mess that would result.
Are the court and Chief Justice John Roberts willing to accept responsibility for that mess? We will find out in June, when a decision is expected on the arguments being made Wednesday.