Tuesday was an emotional day for the left.

In the morning President Obama nominated Sonia Sotomayor to the United States Supreme Court. It was welcome news for those of us who’d hoped for a liberal, woman of color to fill the vacancy. After taking a battering on economic bailouts, torture, and don’t-ask-don’t tell, it was nice to feel as though President Obama was unapologetically siding with progressive interests.

As personal celebration I repeatedly played the classic track South Bronx by legendary hip-hop artist KRS-One at top volume in my office. It seemed like a generationally appropriate way to express my enthusiasm about a smart, self-made, progressive Puerto Rican woman judge being nominated to the court by a smart, self-made, centrist African American President.

My mood, and that of many on the left, became more somber in the afternoon when we learned that the California Supreme Court chose to uphold Proposition 8’s ban on same-sex marriage. Hip-hop no longer felt like the right soundtrack for the day.

But it is possible that we have it all wrong. Maybe we ought to be celebrating the regressive decision by the California court and somberly receiving news of the Sotomayor nomination.

I spent seven years on the faculty of the University of Chicago and shared a hallway with Professor Gerald Rosenberg. His field defining text, The Hollow Hope, argues that the courts rarely bring about social change. Somewhat counter intuitively Rosenberg argues that Supreme Court decisions can work against progressive political interests because a major "win" can leave activists complacent while encouraging opponents to redouble their efforts. By this interpretation the courts are at best a blunt instrument of social change, and at worst they generate ideological and organizational backlash that can harm rather than help social movements.

There was clearly some evidence of this effect today. Some have argued that the massive popularity of candidate Obama in California during the general election lulled some marriage equality advocates into undue optimism that Proposition 8 would fail. Certainly no such complacency existed today. Marriage equality advocates took to the streets in cities and towns across the country. Activists are organized for state-by-state campaigns to topple unequal practices. Social networks and new media are buzzing with activity. In twenty years we may well remember this California decision as a key moment that turned the tide in public opinion and organizational capacity for same sex marriage rights.

Alternately, it is hard to predict the impact that Sotomayor will have on American judicial history. She is a left of center judge replacing a justice who was also reliably left of center. Though undoubtedly her Latina identity is meaningful and historic, it is also not deterministic of her judicial temperament or predictive of her future decisions. To assume otherwise is both foolish and racist.

And even if Sotomayor proves a doggedly progressive presence on the court, Rosenberg’s thesis warns that the symbol of her nomination may serve as a rallying point for conservative interests. Sotomayor could be deployed as a kind of Supreme Court "boogie man" to reinvigorate the GOP’s socially conservative base in anticipation of the 2010 midterm elections.

I think Sotomayor is the right choice for the Supreme Court and I believe that California’s court made the wrong choice on marriage equality. But seven years of sharing a hall with Gerry has me convinced that history may tell a different story.