If Edward Snowden gave federal courts the means to declare the National Security Agency’s data-gathering unconstitutional, Sonia Sotomayor showed them how.

It was Sotomayor’s lonely concurrence in U.S. v Jones, a case involving warrantless use of a GPS tracker on a suspect’s car, that the George W. Bush-appointed Judge Richard Leon relied on when he ruled that the program was likely unconstitutional last week. It was that same concurrence the White House appointed review board on surveillance policy cited when it concluded government surveillance should be scaled back.

“It may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties,” Sotomayor wrote in 2012. “This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks.”

Not a single other member of the high court signed onto Sotomayor’s concurrence; her three Democratic appointed colleagues sided with a narrower one written by Justice Samuel Alito. Though all nine justices agreed that police would likely need to get a warrant to place a GPS device on a suspect’s car, it was Sotomayor who was willing to argue that modern technology had essentially changed the meaning of what privacy means when so much of our personal information and history is preserved online, and can be easily collected by the government in mass quantities. When the Framers of the Constitution wrote of “persons, houses, papers, and effects,” they could not have imagined cloud storage or cell phone location tracking.

The legal challenges to the NSA’s metadata program may never reach the Supreme Court. But if they do, the high court will have to reckon with Sotomayor’s reasoning in Jones.

“Sotomayor’s concurrence in Jones is already proving to be extremely influential,” says Adam Winkler, a law professor at the UCLA School of Law. “Sotomayor was willing to face up to the challenges of new technology, that people still have a right to privacy even if they’re giving up information to a cell phone provider or doing a search on Google.” More than just a legal opinion, Sotomayor penned a legal manifesto on privacy for a digital age debated among Fourth Amendment scholars and brandished by civil libertarians seeking to prevent the coming of a digital government panopticon.

“GPS monitoring generates a precise, comprehensive record of a person’s public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations,” Sotomayor wrote–a description that could easily be applied to all sorts of digital records. Judge Leon cited that sentence in his ruling that the NSA’s metadata gathering was likely unconstitutional, explaining how “[r]ecords that once would have revealed a few scattered tiles of information about a person now reveal an entire mosaic–a vibrant and constantly updating picture of the person’s life.”

The legal argument behind the NSA’s data-gathering is based in part on long-standing Fourth Amendment doctrine that when we give up information to third parties like the phone company, it’s no longer private. Civil liberties groups had long argued that view was increasingly anachronistic, but it was Sotomayor’s concurrence that, for the first time, gave those theories the legitimacy that comes with being adopted by a member of the high court. Sotomayor would provide civil liberties groups with a firm hand-hold as they sought to challenge the government’s warrantless acquisition of all types of digital records, from cell tower data to the NSA’s metadata program.

“Justice Sotomayor’s concurrence in Jones was the first time a Supreme Court justice seemed to acknowledge and speak directly to that new reality,” said Catherine Crump of the ACLU, who helped write the group’s Supreme Court brief in Jones. “To have a Supreme Court Justice acknowledge that there is a difference between a few discrete pieces of information about someone and the complete records you can now gather in the era of big data made us feel like we were on the right path.”

Winkler compared Sotomayor’s concurrence in Jones to Justice Louis Brandeis’ concurrence in Whitney v. California, whose expansive interpretation of the First Amendment we now take for granted. “I think that Sotomayor’s concurrence is going to be seen much the same way,” Winkler said.

If it seems ironic that a justice appointed by President Obama may have lit a legal path to overturning his own surveillance policy, the greater shock should belong to Sotomayor’s early detractors. When Obama first tapped Sotomayor in 2009, she was savaged as an intellectual lightweight, an affirmative action baby who would never be able to write the sort of far-sighted dissents or concurrences that might persuade judges appointed by the opposite party or potentially become law. That is, the exact sort of concurrence she penned in Jones.

When the woman who would become the first Latina Supreme Court justice wasn’t being attacked as an anti-white racist by the likes of National Journal columnist Stuart Taylor Jr. or former House Speaker Newt Gingrich, leading liberal legal minds were wringing their hands about her supposed lack of sophistication or intelligence. In a 2009 article for The New Republic, Jeffrey Rosen quoted anonymous sources questioning Sotomayor’s intelligence and wondered whether she met the “demanding standard” for a Supreme Court Justice. Sotomayor, Harvard Law Professor Laurence Tribe wrote to Obama, is “not nearly as smart as she seems to think she is,” and her “reputation for being something of a bully could well make her liberal impulses backfire” and alienate potential swing votes from the conservative wing of the court.

Rosen didn’t respond to a request for comment from msnbc. Tribe however, acknowledged underestimating Sotomayor.

“I greatly underestimated how powerful a jurist Justice Sotomayor would be. From the start, she has been an enormously impressive justice, making a major impact in cases like Jones, among many others,” Tribe wrote in an email. “I now regard her as a major force on the Court – someone who is likely to make a historic contribution – and I have no doubt that I was totally wrong in my initial expressions of doubt.”

Doubt is nothing new for Sotomayor, a graduate of Princeton and Yale by way of the South Bronx. At Princeton in the 1970s, she wrote in her memoir My Beloved World, letters to the student paper often lamented “the presence on campus of ‘affirmative action students,’ each one of whom had presumably displaced a far more deserving affluent white male and could rightly be expected to crash into the gutter built of her own unrealistic aspirations.” Ultimately it was their expectations of her that turned out to be unrealistic.

“Justice Sotomayor has been underestimated at every stage of her life,” says Winkler. “Sotomayor was underestimated in part because she was the first Latina, it was easy to say she didn’t have the skills and she was an affirmative action baby, but it was an absurd claim then and it’s now being shown to be absurd.”