Clear and Present Danger
Before this was a Tom Clancy novel (1989) and subsequent film (1994), it was a phrase taken from a landmark Supreme Court decision.
In 1919, Justice Oliver Wendell Holmes wrote an opinion for a unanimous court in Schenck vs. United States. Two people were arrested for distributing pamphlets encouraging resistance to the draft for World War I. They were charged with violating the Espionage Act of 1917. They claimed the arrest violated their First Amendment rights.
Holmes wrote that the state could restrict speech:
[…] if the words used are used in such circumstances and are of such a nature as to create a clear and present danger that they will bring about the substantive evils that Congress has a right to prevent
Holmes felt that the defendants actions posed a “clear and present danger” to the United States, because they were encouraging people to commit a crime that might jeopardize national security, so their speech could be restricted.
Just a few weeks later, in Abrams vs. United States, Holmes went the other way. The defendants threw leaflets from a building denouncing the war. They were also charged under the Espionage Act of 1917. In that case, Holmes wrote (in a 7-2 dissenting opinion) that these actions did not pose a danger to the United States. Expression of personal opinions is allowable speech.
This phrase took of a life of its own, and was used to justify that the government could infringe on individual rights that posed a danger to the country or its citizens. It became an informal standard for evaluating whether speech was permissible.
Since then, the phrase was modified and watered down through subsequent opinions and rulings.
In 1969, the standard was essentially replaced in Brandenburg v. Ohio with another phrase:
[The Constitutions does] not permit a State to forbid or proscribe advocacy of the use of force or of law violation except where such advocacy is directed to inciting or producing imminent lawless action
“Imminent lawless action” became known as “the Brandenburg test,” and it remains the de facto standard today.
Why I Looked It Up
I’ve been buying the Tom Clancy novels of my high school years. I knew the phrase had some meaning beyond the title of the book, so I looked it up.