While the controversy surrounding Edward Snowden's dissemination of National Security Agency information continues, members of Congress, journalists and advocacy groups keep repeating the same argument: Mr. Snowden should turn himself in, mount a solid defense and all will be righted at trial.

That's a fantasy. I served as legal adviser to two high-profile whistleblowers between 2010 and 2013, former NSA senior executive Thomas Drake and former CIA officer John Kiriakou, both charged with espionage. I also witnessed last year's...