Glenn Greenwald is a columnist for The Guardian, a former constitutional lawyer and the author of four books, most recently "With Liberty and Justice for Some."

President Obama has repeatedly hailed himself for presiding over "the most transparent administration ever." At the same time, he has waged a sustained and unprecedented war on whistleblowers, press freedoms and the basic mechanisms of the newsgathering process.

But it is the administration of Barack Obama that has prosecuted more accused leakers under "espionage" statutes than all prior administrations combined -- in fact, double the number of all prior such prosecutions.

A climate of fear is keeping journalists from doing their job -- informing citizens about the secret actions of political leaders.

This is the vital context in which the Obama Justice Department's conduct regarding both The A.P. and Fox News' James Rosen must be understood. Time and again, this administration has proven that it has little other than contempt for time-honored protections to safeguard whistleblowing and transparency.

It tried to impose a lengthy prison term on Thomas Drake, a former National Security Agency official who exposed serious agency corruption and wrongdoing, only for its case to fall apart shortly before trial. A formal United Nations investigation found that its detention treatment of Bradley Manning, who exposed multiple acts of serious government deceit and wrongdoing, was so abusive that it amounted to "cruel and inhuman" treatment.

While President Obama aggressively protected Bush officials from any liability for the creation of a worldwide torture regime, his Justice Department prosecuted and imprisoned a former C.I.A. official, John Kiriakou, who publicly condemned torture. It has convened a grand jury to criminally investigate WikiLeaks for doing what media outlets do every day -- publishing classified information that it received a from a government source -- and to do so, embraced a theory of criminality pioneered by Richard Nixon when he sought to prosecute a New York Times reporter for publishing the Pentagon Papers.

In The A.P. case, the Obama Justice Department flagrantly violated long-standing procedures, and its own internal guidelines, by obtaining weeks of office and home telephone records of multiple A.P. journalists without notifying the media organization in advance, thus depriving them of the opportunity to obtain a court ruling on the propriety of the government's actions. And now, in the most disturbing episode yet, it has formally accused another journalist, Fox's Rosen, of being a "conspirator" in a serious felony for doing nothing more than what investigative journalists do every day: work with their government sources to receive classified information that they can then publish for their readers.

This now-lengthy pattern has two primary effects. First, it creates a serious climate of fear in which investigative journalists are finding it increasingly difficult to do their job -- informing citizens about the secret actions of political leaders -- because everyone involved in that process is petrified of government persecution. As The New Yorker's Jane Mayer put it in a New Republic article detailing the harm done to journalism: "It's a huge impediment to reporting, and so chilling isn't quite strong enough, it's more like freezing the whole process into a standstill."

Second, it establishes a standard where the only information the public can learn is what the U.S. government wants it to know, which is another way of saying that a classic propaganda model has been created.

The 2008 version of Candidate Obama was absolutely right when he decreed that government whistleblowers are engaged in "acts of courage and patriotism" that "should be encouraged rather than stifled." The presidential version of Obama is wrong -- dangerously so -- in his still escalating assault on the sources and journalists who make that possible.