As the Senate was considering his nomination to become this nation's 17th chief justice, John Roberts—once a star pupil in my constitutional law class—famously compared the role of a judge with that of an umpire, just calling the balls and strikes. In many respects, that analogy is a deeply flawed one. Constitutional rules are not black and white; there are many shades of grey in between, and it’s up to our highest court both to define the strike zone and to interpret the rules themselves. It is simply unrealistic to say that judges can decide every case by mechanically applying a rigid algorithm. If they could, we wouldn’t need nine justices on our highest court and could probably program computers to do their work.

In one respect, however, the analogy is a sound one. Umpires should not care who wins: the home team or the visitors. So, too, judges should not care who wins: Republicans or Democrats.

That ideal of neutrality, many Americans believed, was shattered in Bush v. Gore. Cynics suggested that the court's 5–4 decision to award the presidency to George W. Bush was more a matter of politics than law. Judges, a lot of people concluded, were rooting for one of the teams. Having argued and lost that case, I wasn’t personally convinced that things were quite that bad, but what counted more in the long run was that the public was. The court's 2010 decision in Citizens United v. Federal Election Commission, which unleashed a torrent of corporate and eccentric billionaire expenditures on politics, only worsened the problem, turning wealth and power into engines of self-replication through the machinery of political contributions: in the ruling’s wake, those with political power have taken on a lopsided indebtedness to those with financial influence.

But today, Chief Justice Roberts has done much to repair the enormous damage done to the Court’s reputation by Bush v. Gore and exacerbated by Citizens United. The Supreme Court's precedents clearly establish that the individual mandate, which doesn’t literally force anyone to purchase health insurance but simply adjusts the income-tax liability of those who don’t, can be sustained as an exercise of Congress's indisputably broad power to impose taxes. By faithfully applying those precedents—regardless of whatever personal distaste he may have had for the law he upheld—the chief justice helped restore Americans' confidence in the political neutrality of their highest court.

That is no small achievement. It is in some ways comparable to what our greatest chief justice, John Marshall, achieved in his landmark 19th-century rulings in Marbury v. Madison and McCulloch v. Maryland. Marbury established the power of the Supreme Court to sit in judgment on the constitutionality of the actions of the other political branches, and McCulloch established the breadth of the political authority entrusted to those branches by the provisions of the Constitution.

As Alexander Hamilton famously said in Federalist No. 78, the Supreme Court has no control over "either the sword or the purse; no direction either of the strength or of the wealth of the society." Its only real power is the power of reason and persuasion, and it is the public that is the ultimate judge of what counts as persuasive. The court depends on its public legitimacy for the efficacy of its decisions. By upholding the mandate, the chief justice reinforced that legitimacy, for he vividly demonstrated that—not unlike a good umpire—he is committed to reaching the correct decision regardless of which side wins.

The result of this case—and the path along which the court moved in reaching it—perhaps comes as a surprise to many observers. But it shouldn’t. During the oral arguments, the chief justice made it clear to anyone who was willing to listen with an open mind that he was inclined to view the mandate as a tax. I had also taken that view in a 2011 Boston Globe editorial, in which I argued: "[T]his law doesn’t literally force anybody to do anything; it just increases the tax liability of those who refuse to buy insurance.” The chief justice evidently saw it much the same way; at oral argument, he mused: “You know, buy insurance or else. Or else what? Or else nothing”—nothing, that is, except a modest increase in one's tax liability, an increase so small that in most instances it would be cheaper for the individual to pay the added tax than to comply with the supposed “mandate.”

Of course, what the court got right should not obscure what it got wrong. The chief justice concluded—unnecessarily, in light of his resolution of the tax power issue—that the mandate could not be sustained under the Commerce Clause, either taken on its own or augmented by the Necessary and Proper Clause. The chief justice reasoned that, while the Constitution authorizes Congress to regulate commercial activity, it does not permit the regulation of commercial inactivity.

What is the source of this curious distinction? According to the chief justice, the difference "between doing something and doing nothing would not have been lost on the Framers, who were 'practical statesmen,' not metaphysical philosophers." That argument gets it exactly backward: the idea that "activity" and "inactivity" are fundamentally different seems to be more metaphysical than practical, not the other way around. In any event, the chief justice overlooked the inconvenient fact that the framing generation actually enacted a bevy of mandates. In 1792, for example, no less a founder than President George Washington signed a law mandating that every able-bodied man buy firearms. As "practical statesmen," the Framers obviously recognized that the good of the nation sometimes called upon Congress to require people to purchase things, even when it might be theoretically possible for the government to make the purchases for them.

Whether the chief justice's unnecessary disquisition on the Commerce Clause will have a long-term effect on Supreme Court doctrine—and an effect that I, at least, would regard as deleterious in a world that demands broad national legislative power to cope with national economic problems—plainly remains to be seen. Much depends on which justices the next president puts on the bench, and thus, in no small part, on just who that president is.

For now, however, this Chief Justice should be roundly applauded for his statesmanlike decision to uphold a law that many in his party, and many who share his ideology, not only deeply dislike but also genuinely believe to be pernicious—despite the fact that the law’s basic design is one that can be directly traced to the work of those very politicians.

That judicial decision, one that would not have been possible without the position formulated and the vote taken and the reasoning provided by Chief Justice John Roberts, will do much to restore and promote the institutional legitimacy of the court he now leads.

That court exists in a system of government that depends deeply on a publicly trusted and politically independent judicial branch to define and police the boundaries of that system’s architecture, and to protect the rights of those that the system itself (or temporary majorities of the electorate) might otherwise oppress.