The Supreme Court's decision upholding the health care law is not only a huge victory for President Obama, but also a moment of leadership for Chief Justice John Roberts. The court's mixed verdict could create problems, notably in its weakening of the law's Medicaid provisions in the name of states' rights. While the impact of this part of the ruling is not fully clear yet, the court may have effectively denied health care coverage to a large number of poorer Americans.

But the headline victory for the law was of enormous importance to Obama. Had the court knocked down the Affordable Care Act, all the spin in the world could not have undone the damage that would have been inflicted on the president and his political standing. Thanks to this ruling, the broad structure of the largest domestic achievement of the Obama legacy remains intact. It gives him bragging rights in the campaign, and in history. And for those who support universal coverage, the fact that the law remains on the books offers an opportunity to build on it in the future.

And Obama was wise to use his address to the nation on the court's decision to restart the effort to explain what the Affordable Care Act actually does and the benefits it offers to Americans who already have health insurance, those who are worried about losing it, and those who would like to get it but cannot now afford it. By putting the health care law at the center of the news, the court case gave the president and other supporters a second chance to do what they should have done more effectively in the first place. It was a nice touch for Obama to try to turn the law's low rating in the polls to his benefit. "It should be pretty clear by now," he said, "that I didn't do this because it was good politics." He was also smart to speak briefly, and to avoid triumphalism.

But if it was Obama's day, the day also belonged to Roberts. Ever since he took the helm at the court, Roberts' critics -- and I have certainly been a vociferous one -- have seen him as failing to live up to the implicit promises he offered during his confirmation hearings to a brand of judicial moderation.

This decision is not as clean and clear as it should have been. But by spearheading a plurality opinion that at least recognizes the power of Congress to legislate on an important social and economic problem, Roberts avoided the far shoals of conservative ideology. He sought to avoid a direct confrontation with the executive and legislative branches.

Roberts' rulings on Citizens United and a variety of labor and regulatory issues fed fears that he would happily take on the role as the leader of a right-wing judicial revolution -- and there is still reason to worry that this is exactly what he'll do on many other issues, notably affirmative action.

But on health care, Roberts chose to blunt these attacks. He cast himself as a jurist sensitive to the obligation of the courts to show at least some deference to the government's elected branches on matters of social policy. He took what might have been a center-left decision upholding the entire law and nudged it to the center or center-right. What he did not do -- and this is to his credit -- was join the right end of the court that wanted to gut the act.

Still, it is disturbing that the court, including Roberts, appears to have weakened the law's provisions that sought to use Medicaid to push states to help to insure many more Americans. Medicaid is a federal law giving the states a great deal of federal money. There is no entitlement to this money. It seemed reasonable for the federal government to use a federally created program to push for the national goal of providing health insurance for all Americans. Before liberals heap praise on Roberts and conservatives declare him a sellout, both sides need to come to terms with the meaning of this part of the ruling.

Overall, it was a good day for President Obama and for Chief Justice Roberts. And with the court so closely divided, it also underscored the importance of the judicial appointments that the president elected (or re-elected) this November will make. We are, it turns out, still one vote away from total conservative dominance on judicial questions. And this is why the health care law survived.

(c) 2012, Washington Post Writers Group