In the American way of government, it often takes an independent-minded judge to tell truth to power. That’s the way the system works. The executive branch is almost always dominated by the exigencies of the day; the legislature—on matters of national security, especially—is often supine. Thanks to the Founding Fathers, federal judges are empowered with the job security and the leeway to think for themselves. And on occasion, thank the Lord, some of them exercise these freedoms.

I am talking here of the workaday jurists who deal with the public on a daily basis, not the well-connected grandees of the Supreme Court, who usually grab the headlines. To this day, the most famous of them is Judge Learned Hand, a well-born son of Albany who spent fifteen years in the federal courthouse of the Southern District of New York, and another thirty-seven years on the United States Court of Appeals for the Second Circuit. More recently, there have been other notable judges, of course, including Jed Rakoff, also of the Southern District, who, in 2011, threw out a settlement between the Securities and Exchange Commission and Citigroup because it didn’t contain any admission of wrongdoing on behalf of the big bank—this despite the fact that the bank stood accused of defrauding investors in a mortgage-bond offering.

Now comes Judge Richard J. Leon, who sits on the federal court in the District of Columbia. Leon has ruled that the National Security Agency’s routine collection of phone records from hundreds of millions of Americans “infringes on ‘that degree of privacy’ that the founders enshrined in the Fourth Amendment,” which prohibits the government from carrying out unreasonable searches and seizures.

In some ways, it should be noted at the outset, Leon and Hand were practically opposites. A Republican conservative who worked in the Justice Department during the Reagan years, Leon also served as special counsel to the House Banking Committee’s Whitewater investigation, before George W. Bush appointed him to the federal bench, in 2001. Hand was a lifelong progressive. Early on, he supported Teddy Roosevelt. A bit later, he helped Herbert Croly to found The New Republic, for which he wrote a number of articles. As judges, what is common to Hand and Leon is a strong suspicion of the federal government encroaching on ancient liberties.

During the First World War, when Hand was still a district-court judge, he struck down parts of the Espionage Act, a precursor to the Patriot Act, which had proscribed any actions that hindered the war effort, including the circulation of seditious materials. Citing the First Amendment, Hand defended the publication of The Masses, a left-wing journal that was stridently anti-war. According to Gerald Gunther, the late constitutional scholar who wrote a lengthy and widely praised biography of Hand, the arguments he made in the The Masses case played an important role in persuading the Supreme Court to strengthen freedom-of-speech statutes.

Most of Leon’s rulings have attracted less notice, but some of them were notable, nonetheless. In an article in Tuesday’s Times, Sheryl Gay Stolberg recalls that, in 2010, he threw out an obscenity case involving a Californian pornographer; in 2012, he barred the use of imported barbiturates used in executions; and, in 2008, he ruled that five Algerians had been illegally detained in the Guantánamo Bay prison camp and ordered the government to free them.

In describing the N.S.A.’s snooping as “almost Orwellian,” and in suggesting that James Madison would be “aghast,” Judge Leon has queried the legitimacy of domestic-surveillance policies authorized by not one but two Presidents. Like all dissident voices, his will be subjected to attacks. In an important sense, though, he has merely stated what should be obvious to anybody who hasn’t swallowed the tendentious justifications offered up by the Bush and Obama Administrations: in the wake of 9/11, the U.S. government moved in a profoundly authoritarian and illiberal direction.

The process of seeking to undermine the ruling has already begun. If you read some of the online commentary on Leon’s sixty-eight-page ruling, you will see suggestions that he is a maverick, an unhinged libertarian, and a judge who doesn’t understand the law. That is only to be expected. After Edward Snowden showed how far the surveillance state had extended its tentacles, he was described as a kook, a traitor, or, worst of all, a mere “contractor” who had no right to question the wisdom of his superiors and his government. This very weekend, Bill Richardson, the former Energy Secretary and U.S. Ambassador to the United Nations, was on “Meet the Press,” repeating this dismissive line.

On the same show, General Michael Hayden, a former head of the N.S.A., defended the actions of the agency, saying,

There is no abuse. And, by the way, I don’t see any unlawfulness either. This is all done according to the Madisonian formula. The President authorized, the legislature legislated, and the courts oversaw. Now, we can have a legitimate argument among free people as to whether or not it’s wise, as to whether or not we generally agree it’s a proper balance between liberty and security. But there were no abuses.

But this, of course, is the very argument that Judge Leon has sought to dismantle. In granting the plaintiffs legal standing to sue the government on the grounds that they, most likely, had had their phone records seized, he breached the wall that had kept the legal arguments about domestic surveillance confined inside the secretive FISA court that has generally served as a rubber stamp for the authorities. And in rejecting the Administration’s argument that bulk collection of phone data is allowed under a 1979 Supreme Court ruling in the case of Smith v. Maryland, Leon has invited higher courts, and ultimately the Supreme Court, to revisit the entire issue of how privacy can be defined, and protected, in the information age.

Of course, the appeals court, to which the Administration will now hasten, could toss out Judge Leon’s ruling, and, if the plaintiffs appeal that ruling, the Supreme Court, as it has done in the past, could refuse to hear a domestic-surveillance case. But Judge Leon’s arguments, which were artfully constructed, will not be so easily dismissed. Rather than challenging the FISA court head on, he accepted the government’s argument that he didn’t have the authority to decide whether it had overstepped its bounds in approving government orders that forced telephone companies, such as Verizon and AT&T, to turn over customer records. Where Judge Leon sought to make his stand was in the more open ground where the legacy of the Founding Fathers meets contemporary policies and realities. On the issue of whether the government’s conduct was constitutional, he asserted that his court had a right to rule, and he reached the conclusion that, most likely, it wasn’t.

In composing his ruling, Judge Leon followed in the spirit of Hand, a famously eloquent writer, by supplementing his citations of legal precedents with broader arguments expressed in clear, and occasionally vivid, prose. He began, as he had to, by acknowledging the force of the Smith v. Maryland ruling, in which the Supreme Court said that a suspected criminal had no reasonable expectation of privacy in the numbers he dialled from his home phone because he transmitted them to the phone company voluntarily, and in the knowledge that the company recorded them as part of its business records. But then, Judge Leon went on: