Final answer:
The Supreme Court case Schenck v. United States in 1919 established the limit to freedom of speech with the phrase "A clear and present danger."
Step-by-step explanation:
In Schenck v. United States in 1919, the quotation used to describe a limit to freedom of speech was "A clear and present danger". This phrase, introduced by Justice Oliver Wendell Holmes Jr., stated that speech could be restricted if it presented a clear and present danger to public safety or harm. The case involved the distribution of anti-draft pamphlets during World War I, and the Supreme Court upheld the conviction of Schenck, arguing that his actions posed a clear and present danger.
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