Writing for the majority of the Supreme Court in United States v. Windsor, Justice Kennedy stated that “[t]he Constitution’s guarantee of equality ‘must at the very least mean that a bare congressional desire to harm a politically unpopular group cannot’ justify disparate treatment of that group.” Under this test, the Court struck down a key provision from the so-called Defense of Marriage Act (DOMA), which defined “marriage” and “spouse” for purposes of federal law as referring only to opposite-sex marriages and spouses. The opinion concludes that DOMA’s very object was “to ensure that if any State decides to recognize same-sex marriages, those unions will be treated as second-class marriages for purposes of federal law.”

It is almost trite to say that the result in Windsor would have been unthinkable just a few years ago. Yet this observation strikes at the heart of a paradox in the test applied by the Court: It suggests that a group has a realistic chance of being classified as a “politically unpopular group” deserving of protection only after it has acquired a certain level of popularity. Of course, the recent shift in popular opinion on same-sex marriage in the United States has been spectacular. In 2004, bans on same-sex marriage (and in many cases, also civil unions and other contractual protections of same-sex relationships) were adopted by popular vote in all of the eleven States where such bans had been put on the ballot during the general elections. Today, the States that have same-sex marriage bans on the books outnumber the States in which same-sex marriage is legalized by thirty-five to twelve (plus D.C.). Yet starting in 2010 or 2011, nationwide support for same-sex marriage began to exceed opposition to it. The increased popularity of the cause translated into political action: In 2012, for the first time voters approved initiatives to legalize same-sex marriage in three States (Maine, Maryland, and Washington). In that same year, voters in Minnesota voted down a proposed same-sex marriage ban. In sum, it is safe to say marriage equality has become a mainstream cause, albeit one that is still met with ardent opposition.

Against this background, the majority ruling in Windsor—while having major practical implications and expressive significance—shows the Court not as a leader, but rather as a careful follower of what has become the prevailing opinion in the United States. The interplay between Supreme Court decisions and societal norms is, of course, one of the overarching topics in the study of constitutional law. And one would expect that nobody feels the pressure of public opinion as acutely as a Justice who is in the position of swing vote. In his book The Nine (which you should read if you haven’t already), Jeffrey Toobin wrote about Justice O’Connor that “[s]he had an uncanny ear for American public opinion, and she kept her rulings closely tethered to what most people wanted or at least would accept.” The notion that judicial rulings are heavily influenced by popular beliefs is troubling to those who believe judges should be constrained by a principled approach to interpretation. Yet it should be equally troubling to those who believe it is a fundamental role of the judiciary to protect unpopular groups from the tyranny of the majority.

For supporters of marriage equality, including myself, DOMA’s partial demise is a cause for celebration. But the Act’s trajectory also offers occasion for introspection, especially for those of us whose views have “evolved” over time. How many were outraged by DOMA before marriage equality became a popular cause? Why did it take quite a few of us several years to see the hatefulness of DOMA that seems so obvious now? If the reason is that we didn’t pay attention, is that simply another way of saying we were indifferent? And, most importantly: Which unpopular groups are currently suffering marginalization or discrimination without the rest of us caring or even noticing?