John Roberts does Obama a favor.

In 2006, at the end of his first term on the Supreme Court, John Roberts told me and other journalists that his goal as chief justice would be to promote unanimity and collegiality by encouraging his fellow justices to converge around narrow decisions with few dissents. During his first term, Roberts succeeded impressively: More than half of the Court's opinions were unanimous, and only 13 percent were decided by a 5-4 vote.The polarized Supreme Court term that ended last June, however, looked very different. Only 38 percent of the Court's decisions were unanimous, and 33 percent were decided 5-4, the highest percentage in recent years. Moreover, in cases striking down affirmative action and campaign finance reform, Roberts and his dissenting colleagues attacked each other in unusually personal terms. Noting this, some liberal bloggers and journalists argued that Roberts's call for unanimity had been a charade. Emily Bazelon of Slate wrote that Roberts didn't actually care about "unity and restraint" and that he would become only more extreme over time. Bazelon's judgment was premature. Although this Supreme Court term isn't over, it's already shaping up to be something of a bipartisan lovefest. "Where have all the 5-4 decisions gone?" asks Linda Greenhouse of The New York Times. As of this writing, nearly 40 percent of this term's decisions were unanimous, and only 14 percent were decided by 5-4 splits. Even more tellingly, some of the term's more controversial decisions--including those involving lethal injections, voter identification laws, federal efforts to curb child pornography, and Iraqi detentions--were unanimous or decided by lopsided, bipartisan majorities. True, there have been a handful of high-profile 5-4 decisions along familiar ideological lines, such as the case extending the writ of habeas corpus to inmates at Guantanamo Bay--and there may well be more in the final weeks of the term--but they have been the exception, not the rule. It's still too early to judge Roberts's tenure, but it seems increasingly clear that liberals dodged a bullet when President Bush nominated him to be chief justice. Instead of siding with conservative extremists like Clarence Thomas, who are eager to press the limits of the so-called Constitution in Exile, resurrecting limits on federal power whenever possible, Roberts prefers narrow opinions that can attract support from the center. Liberals ought to applaud this instinct because, even if Barack Obama gets to appoint the next justice or two, it's the only thing standing between them and a Court eager to roll back progressive reforms. Why was Roberts successful in uniting the Court this year? Part of the reason, as Orin Kerr of George Washington University recently observed, is that he has done exactly what he said he would do in 2006: namely, convince moderate liberals and conservatives that unanimity is in their interest. In particular, Roberts has been more willing than his predecessor to assign plurality (rather than majority) opinions. In these cases, Roberts begins with the three center- right conservatives (himself, Anthony Kennedy, and Samuel Alito) and tries to attract liberal justices to a narrowly reasoned decision, while letting the hard-line conservatives (Thomas and Antonin Scalia) write separate, more extreme concurrences. In cases with no majority opinion, the narrowest opinion for the winning side has to be followed as if it were the majority opinion. Roberts has followed this strategy--finding a "sweet spot," as Kerr puts it, by "aiming toward the middle"--in the recent 7-2 and 6-3 cases upholding lethal injections and voter ID requirements. In both cases, the Court issued a moderately conservative controlling opinion joined by one or two liberal justices, followed by more extreme concurrences by Scalia and Thomas. Roberts has also promoted unanimity by encouraging the Court to hear more business cases, in which the justices tend not to divide along ideological lines. Roberts told me that unanimity in less high-profile cases could promote "a culture and an ethos that says, 'It's good when we're all together,'" and that's exactly what the business cases--which represent about 45 percent of the court's docket this year--have achieved. Out of 14 cases in which the U.S. Chamber of Commerce filed briefs this year, 86 percent have already been decided by margins of 7-2 or better and over one- third have been unanimous. During a tnr town-hall interview in March, Justice Stephen Breyer explained that cases involving the interpretation of federal statutes were often less divisive than constitutional cases because they turn on more technical questions about which the justices don't have strong pre- existing views. He also said that when a decision was nearly unanimous, he was inclined to think: "Maybe that was the right answer!" In cases where the justices do have strong constitutional views, such as the decision last week involving habeas corpus at Guantanamo, the familiar 5-4 ideological divisions persist. But, even in the Guantanamo case, Roberts dissented from the majority opinion in far more measured terms than he had used to criticize Breyer's dissent in the affirmative action case last year. Avoiding Scalia's hysterical claim that this decision "will almost certainly cause more Americans to be killed"--an assertion unsupported by anything in the government's brief--Roberts respectfully argued that the liberal justices themselves had previously suggested that Congress, rather than the courts, should decide detention policy. Similarly, Justice John Paul Stevens's willingness to side with the moderate conservatives in the voter ID, lethal injection, and child pornography cases suggests that he, too, has concluded that constructive engagement is better than 5-4 polarization when a narrowly reasoned opinion may leave the door open for liberal victories down the road. In their eagerness to dismiss Roberts as a hypocrite, liberal critics have suggested that it doesn't matter whether conservative opinions are based on narrow or broad reasoning; all that matters is the bottom line. But this judgment, too, is shortsighted. Even if Obama wins the White House and has the opportunity to replace one or two retiring liberal justices, the Court's ideological makeup is likely to stay the same for the foreseeable future: four liberals and four conservatives, with Kennedy in the middle. If Roberts succeeds in promoting narrow, bipartisan opinions, the Court is unlikely to resurrect the Constitution in Exile and declare war on a progressive Congress for the first time since the New Deal era. By contrast, if Roberts fails and the Court gets in the habit of handing down sweeping conservative opinions by polarized 5-4 majorities, many of the health care and environmental reforms that progressives hope for from a Democratic president and Congress might be struck down by the Court. As Larry Kramer, the dean of Stanford Law School, puts it, "Once solidly in power, Democrats are more likely to push the envelope in areas like the environment and health," rather than civil liberties, and a conservative court could push back by holding that Congress lacks the power to regulate matters previously left to the private sector. For example, according to Damon Silvers, associate general counsel for the AFL-CIO: "Legislation requiring employers to purchase health insurance for their employees could be challenged by arguments asserting the Constitution includes an unwritten guarantee of freedom of contract that would allow private parties to enter into employment contracts without health insurance." Going forward, Silvers told me, "[t]ax policies and regulations seeking to limit the use of carbon-based fuels could be challenged as a taking of someone's mineral rights." Although Thomas might be sympathetic to these arguments, he and Scalia would remain on the Court's conservative fringe in an Obama administration--but only if Roberts continues to promote narrow opinions that appeal to the center. The presidential election, of course, will determine the future of the Roberts Court. If McCain wins, there will be a lopsided conservative majority, and Roberts will no longer need to win over the one or two liberal justices on the margins. But, if Obama wins, Roberts's success in promoting his vision of unity and minimalism will determine whether the Court blocks a Democratic Congress and White House or whether it lets them pass the laws that the American people expect.