Publishing the Pentagon Papers (1971)
In 1967, the Johnson Administration commissioned a secret study, entitled "History of U.S. Decision-Making Process on Vietnam Policy." The 7,000-page document laid out in scandalous detail the blunders and miscalculations made by the U.S. government in the Vietnam War, including ignoring intelligence assessments and backing corrupt leaders with little support from the Vietnamese populace. Nobody outside the government might have ever seen it, except that RAND Corporation researcher Daniel Ellsberg — frustrated that the report was being ignored — finally gave a copy to New York Times reporter Neil Sheehan.
The Times published the first installment of a series based upon it in June 1971. Johnson's successor in the White House, Richard Nixon, was incensed at the leak. He had his Attorney General, John Mitchell, order the Times to stop publishing information from the report and return it, or face prosecution for espionage.
When the Times refused, Mitchell went to court and sought an injunction. That led to a landmark Supreme Court 6-3 decision, which probably had an even greater impact than the scoop itself. It established that under the First Amendment, the government couldn't prevent the publication of exposés, no matter how embarrassing the facts might be [source: Priest].