C-SpanC-SpanTwo years ago, when Chief Justice John Roberts led the Supreme Court in upholding the constitutionality of the Patient Protection and Affordable Care Act, he justified his decision in terms of judicial restraint. "If there are two possible interpretations of a statute," Roberts wrote, "and one of those interpretations violates the Constitution, the courts should adopt the interpretation that allows the statute to be upheld." Roberts then proceeded to uphold Obamacare by adopting what he called a "saving construction" of the health care law.

Libertarians and conservatives were outraged by Roberts' deferential maneuver—and with good reason. They expected the Supreme Court to follow the Constitution, not tip the scales in favor of a contested federal statute.

The chief justice of the United States performed another act of constitutional avoidance this week in the case of Bond v. United States. At issue was the bizarre prosecution of a Pennsylvania woman named Carol Anne Bond, who was sentenced to six years in federal prison under the terms of the 1998 Chemical Weapons Convention Implementation Act. Her crime? She smeared two toxic chemicals on the doorknob, car door, and mailbox of a woman who had been having an affair with her husband. Bond's victim suffered a slight burn to one hand.

In a surprise twist, this soap opera-like saga raised major questions of federalism and the reach of federal power. According to the Obama administration, its power to make and enforce treaties with foreign governments (such as the Chemical Weapons Convention) was itself sufficient authority to justify the sweeping federal statute deployed against Bond.

Yet as Justice Anthony Kennedy told Solicitor General Donald Verrilli during oral arguments, it "seems unimaginable that you would bring this prosecution." Bond, meanwhile, argued that the 10th Amendment prevented the government from making a federal crime out of her purely local offense.

On Monday the Supreme Court ruled 9-0 in Bond's favor. The Obama administration's "boundless" interpretation of the chemical weapons law, declared the opinion of Chief Justice Roberts, "would transform the statute from one whose core concerns are acts of war, assassination, and terrorism into a massive federal anti-poisoning regime that reaches the simplest of assaults."

Much like he did in the 2012 health care case, however, Roberts then stopped short. Although the text of the federal law plainly criminalized the possession and use of toxic chemicals for non-"peaceful" purposes, Roberts nonetheless construed that text as narrowly as possible, issuing another saving construction that allowed the embattled federal statute to survive unscathed. The Chemical Weapons Convention Implementation Act, he declared, "does not cover the unremarkable local offense at issue here."

In other words, while Bond should not have faced federal charges, the law itself could remain on the books.

To be sure, that outcome was a resounding defeat for the Obama administration, which failed to garner a single vote in favor of its expansive case for federal power. But the outcome could have been far worse for the administration. In fact, Justices Antonin Scalia, Clarence Thomas, and Samuel Alito clearly wanted to make it so. While those three justices also voted in Bond's favor, they refused to sign on to Roberts' rationale. In their view, the chemical weapons law did criminalize Bond's local deeds—and that fact rendered it an unconstitutional exercise of federal power.

"As sweeping and unsettling as the Chemical Weapons Convention Implementation Act of 1998 may be, it is clear beyond doubt that it covers what Bond did," wrote Justice Scalia in a concurring opinion. "So we are forced to decide—there is no way around it—whether the Act's application to what Bond did was constitutional. I would hold that it was not." As Scalia saw it, Roberts' narrow approach was tantamount to an act of judicial surrender. "We should not have shirked our duty and distorted the law," Scalia concluded.

It's common these days for legal observers, especially those on the left, to speak of the Supreme Court's right-leaning justices as if they marched in intellectual lockstep. Linda Greenhouse of The New York Times, for example, recently echoed that liberal narrative in these terms: "I’m finding it impossible to avoid the conclusion that the Republican-appointed majority is committed to harnessing the Supreme Court to an ideological agenda."

Perhaps she should try a little harder before reaching such a facile conclusion. In Bond, as in the health care case before it, the "Republican-appointed majority" had a prime opportunity to declare unconstitutional an overreaching federal law defended by the Obama administration. Yet in both cases, the chief justice broke with his nominal friends on the right, joining instead with the Court's liberals (plus the mercurial Justice Kennedy in Bond) to craft a saving construction that cabined the Court's ruling and avoided a broader constitutional showdown.

For better or worse, John Roberts is marching to a beat of his own.