FORTY years ago today, The New York Times began publishing the Pentagon Papers, a seminal moment not only for freedom of the press but also for the role of whistle-blowers — like Daniel Ellsberg, who leaked the papers to expose the mishandling of the war in Vietnam — in defending our democracy.

Today, the Obama administration is aggressively pursuing leakers. Bradley E. Manning, an Army private, has been imprisoned since May 2010 on suspicion of having passed classified data to the antisecrecy group WikiLeaks. Thomas A. Drake, a former official at the National Security Agency, pleaded guilty Friday to a misdemeanor of misusing the agency’s computer system by providing information to a newspaper reporter.

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