What Supreme Court case ruled that speech causing a "clear and present danger" is not protected under the First Amendment?

The ruling that speech causing a "clear and present danger" is not protected under the First Amendment stems from the Supreme Court case Schenck v. United States, decided in 1919. This case involved Charles Schenck, who had distributed pamphlets urging resistance to the draft during World War I. The Court, in an opinion written by Justice Oliver Wendell Holmes Jr., held that while the First Amendment protects free speech, it does not extend to speech that poses a significant risk of inciting harm or public disorder.

The "clear and present danger" test articulated in this case established a critical standard for determining when the government could limit speech without infringing upon constitutional rights. The specifics surrounding the context of war and the government's need to maintain order were key factors in the Court's decision, reflecting the balance between individual rights and national security concerns during a time of crisis. This precedent has influenced subsequent interpretations of free speech rights in the United States.