JUNE 28th was a day of reckoning for the most important law of Barack Obama's presidency, and for the president himself. The Supreme Court was to decide the fate of Mr Obama's 2,700-page health reform. Oral arguments in March had not proceeded as Democrats had hoped. Mr Obama's lawyer choked on his water, faltered in his opening statement, then endured a battery of hostile questioning. Suddenly it dawned on Democrats that their most treasured achievement might die. 

But when judgment day came the Supreme Court sided with Mr Obama, by five votes to four. John Roberts, the chief justice, joined the court's four liberals in upholding the Democrats' biggest legislative feat in decades. The law requires Americans to buy insurance or pay a penalty—the so-called “individual mandate”. That penalty, the court ruled, falls within Congress's power to tax. The court did impose a rider on the law's expansion of Medicaid, the federal-state health programme for the poor. But the decision is a huge relief for the president and his allies. 

There was little doubt that had the Supreme Court overturned his reform, it would have been mortifying. Mr Obama would have been found guilty by the highest court in the land of an unconstitutional power grab. The president will naturally have something of a spring in his step for the next few weeks. But even so, the victory may be fleeting.

Mr Obama signed the Patient Protection and Affordable Care Act into law on March 23rd 2010. In doing so, he achieved what no other Democrat had: he moved America decisively towards universal health insurance. Within minutes, however, 13 states had filed suit against the law in Florida. Soon others sued elsewhere. The pioneers were joined by the National Federation of Independent Business, four private individuals and 13 more states. In November the Supreme Court announced it would hear the case. 

The challengers insisted that the mandate would bring a “revolution in the relationship between the central government and the governed”. Under the constitution, Congress could no more compel Americans to buy health insurance than it could oblige them to eat broccoli or to buy American cars to support Detroit's manufacturers. Where, in other words, would this latest extension to the power of the federal government end?

The states also complained that the law's expansion of Medicaid—to childless adults with incomes of up to 138% of the federal poverty level—was unduly coercive. If they did not abide by the law's rules, they would lose their federal Medicaid money. It was, in effect, an offer states could not refuse. 

Mr Obama's lawyers presented a more complex case. The constitution gives Congress the power to regulate interstate commerce. Health care is a huge, muddled industry in need of regulation. The sick pay exorbitant rates for insurance, or go without it. In 2009 50m uninsured people consumed health care they could not pay for; the tab was covered, unfairly, by those with insurance. The mandate is a proper way to fix these problems, the president's lawyers argued. What is more, the penalty for not buying insurance falls within Congress's power to tax—even though in 2009, Mr Obama and Democrats insisted the mandate was nothing of the kind. As for Medicaid, Congress regularly ties state funding to particular requirements. 

The majority of the court sided with Mr Obama. Mr Roberts, writing the court's opinion, did not buy Mr Obama's commerce-clause argument. “Construing the commerce clause to permit Congress to regulate individuals precisely because they are doing nothing would open a new and potentially vast domain to congressional authority,” Mr Roberts wrote.

But the mandate, the chief justice explained as he sided with the president's backup argument, may be considered a tax on those without insurance, and Congress has the power to tax. The law does not compel individuals to act; if they do not want insurance, they can simply pay the penalty. Mr Roberts then continued that the government may offer states money to expand their Medicaid programme. “What Congress is not free to do,” he wrote, “is to penalise states that choose not to participate in that new programme by taking away their existing Medicaid funding.” 

Independent of the ruling's impact on health care, the decision fundamentally changes the politics of the Supreme Court. Ever since the five justices appointed by Republican presidents sided with George W. Bush in the disputed election of 2000, Democrats have liked to dismiss the court as biased against them. This argument was always suspect. The court votes 9-0 far more often than it does 5-4. But any claim that the court's Republican appointees will stop at nothing to impose their conservative agenda now seems ludicrous in the light of the chief justice's vote.

So health reform is safe in law, for the time being; but this still does not guarantee that it will be a success on the ground. Implementation of the reform has been patchy. Mr Obama's law requires states to create health exchanges, where individuals may compare and buy insurance, by 2014. Only two states have already set up exchanges, and only 13 more have started to create them. Despite the court's ruling, Republican governors will be in no hurry to follow suit. The Supreme Court may not have overturned the law, but Republicans still plan to do it themselves after ejecting Mr Obama from the White House. 

Their effort will be helped by public opinion. Mr Obama sacrificed other initiatives—including more focused attention on the economy, not to mention immigration reform and climate legislation—for the sake of health care. But the main preoccupation of voters remains the economy. When asked by pollsters to name the issue that worries them most, only 5% or so volunteer health care. Jobs and the economy, in contrast, routinely score 50% or more. 

When voters do consider health reform, they view it in an unfavourable light. Some 50% of the public dislike the law, while only 40% approve. Voters hold an even dimmer view of the law's constitutionality. According to a recent CBS News/New York Times poll, only 24% thought the court should uphold the entire law, 27% thought the mandate should fall and 41% thought the court should scrap the whole thing. 

Diehard opponents of the law will probably be energised by the court's rebuff to them. Republicans have counted “NObamacare” as one of their most effective rallying cries over the past two years. Such chants will now be joined by the lacerating eloquence of the conservative justices' opinions. The ballot box in November, Republicans can now point out, is the only remaining path to repeal. Democrats waited for a decision on health care for over two years. The next period of uncertainty will, at least, be rather shorter.