On the day that Edward Snowden finally left Moscow’s airport in a taxi to take up Russia’s offer of temporary asylum and the sentencing portion of Bradley Manning’s trial continued, it is worth restating what should be obvious. Leaking classified information is a crime, and it can be damaging to the national interest; but, in some circumstances, it can also be a patriotic and useful act that helps bring about necessary reforms.

Setting aside Snowden’s personal odyssey—he’s been holed up at Sheremetyevo Airport since June 23rd—the documents he released detailing the National Security Agency’s spying programs, domestic and global, have already had a transformative effect. For decades, Congress has adopted a hands-off and pusillanimous approach to the N.S.A., appropriating vast sums for its operations—its budget remains classified, but it’s reportedly about ten billion dollars a year—and not examining too closely how this money was spent. As the agency sought to expand its domestic surveillance programs in the aftermath of 9/11, Congress, by passing successive versions of the Patriot Act and other measures, actively enabled it to broaden its remit under the catch-all justification of countering terrorism.

Now, finally, some questioning voices are being raised. In a hearing on Capitol Hill yesterday, senators from both parties interrogated the N.S.A.’s leadership about its justification for mining the phone logs of millions of Americans who aren’t suspected of having any connection to terrorism, saying the agency’s top officials had greatly exaggerated the number of terrorist plots it had thwarted thanks to the program. Patrick Leahy, Democrat of Vermont, said he had been shown a classified list that didn’t indicate “dozens or even several” plots had been detected. Republican Charles Grassley, of Iowa, criticized James Clapper, the director of National Intelligence, for misleading Congress about the phone-log program.

At this stage, it’s far from clear whether the Congressional hearings will lead to any real changes in how the N.S.A. operates. The spectre of being accused of being soft on terrorism still haunts Washington, and it works against any substantial rolling back of the surveillance state. But at least the activities of the electronic spooks are being publicly discussed, and the Obama Administration is being forced to justify the way it has, in the area of domestic spying, continued, and quite possibly expanded, the policies of the Bush Administration. (On Capitol Hill yesterday, Robert S. Litt, a senior lawyer in the Office of the Director of National Intelligence, said the Obama Administration was “open to reëvaluating” the phone-log program while “preserving the essence.”)

It barely needs saying that none of this would have happened had Snowden kept his own counsel about what he saw as the N.S.A.’s gross abuses of privacy, or if he had done what even some people in the media have suggested and registered his concerns to his immediate superiors. By handing over N.S.A. documents to journalists from the Guardian and the Washington Post, he brought to the attention of the American public detailed information about something they have every right to know: their government is spying on them.

Some of what the N.S.A. is doing had been revealed in previous news stories by investigative journalists, notably Eric Lichtblau and James Risen of the Times (who is facing the prospect of going to jail rather than revealing a source in another area). But the wealth of detail in Snowden’s documents, and his revelation of the existence of previously undisclosed spying programs such as Prism, makes ridiculous the suggestion that he didn’t really tell us anything new. At the very least, he told us that the N.S.A.’s surveillance operations are much bigger and more systematic than we previously knew, and that senior officials in the Obama Administration, notably Clapper, have been misleading Congress and the public about them.

Perhaps the most depressing aspect of the Snowden case has been the official effort, going all the way up to Secretary of State John Kerry, to depict him as a traitor. Actually, Snowden appears to be an idealistic young man who had no ill intentions toward his country but who gradually became disillusioned with some of its actions. He enlisted in the Army during the Iraq War because, he told the Guardian’s Glenn Greenwald, “I believed in the goodness of what were were doing,” only to be discharged several months later. Even now, he told Greenwald, he believes that “America is a fundamentally a good country; we have good people with good values who want to do the right thing, but the structures of power that exist are working to their own ends to extend their capability at the expense of the freedom of all publics.”

The Manning case is a bit different. In unearthing a video of a U.S. Apache helicopter firing on civilians in Baghdad, and in publishing details of internal battlefield reports from Iran and Afghanistan, he brought to light military atrocities that would otherwise have remained covered up. But in releasing seven hundred thousand documents to WikiLeaks, including some quarter of a million diplomatic cables, he was far less discriminating than Snowden, leaking, for example, details of cables containing unvarnished assessments of foreign countries, and foreign leaders, from U.S. officials. Other than that it is catnip to journalists, I don’t see much public-interest justification for leaking this sort of information—although some have argued that the cables helped undermine oppressive governments abroad, and may even have been a factor in the Arab Spring. Still, though, there is nothing to suggest that the former Army specialist had any intent to inflict damage on the United States. When he offered, earlier this year, to plead guilty to some of the less serious charges against him, which carried a potential sentence of twenty years in jail, he said he was trying to show his fellow citizens the “day-to-day reality” of America’s wars, and to spark a public debate about U.S. policies in Iraq and Afghanistan.

That doesn’t mean he should have been let off completely. All governments need to keep some things secret, such as diplomatic cables and the details of military plans. That necessitates sanctions against leakers, especially ones whose leaks aren’t restricted to information about official wrongdoing and overreaching. But how severe should those sanctions be? In charging Manning with “aiding the enemy,” a crime that can carry the death sentence, the Pentagon acted in an unprecedented and outlandish manner. Thankfully, Colonel Denise Lind, the military judge in the case, found him not guilty of that charge, though she convicted him on numerous other counts, including leaking classified information and violating the Espionage Act.

We still don’t know for sure what will happen to Snowden or Manning: the former appears destined to a life of exile, for now, at least, in a repressive country; the latter, for many more years in a military jail. (He’s already been in custody for almost three years, including in solitary confinement for eleven months—a treatment that a senior United Nations official charged with investigating allegations of torture described as cruel and inhuman.) We do know that, at great cost to themselves and their families, Snowden and Manning have illuminated much that the authorities would have preferred to keep hidden, and that they have sparked a long overdue public debate about what the Times, in its editorial about the Manning verdict, justly described as “a national security apparatus that has metastasized into a vast and largely unchecked exercise of government secrecy and the overzealous prosecution of those who breach it.” In short, the two leakers have performed a valuable public service.

Photograph by Maxim Shemetov/Reuters