Final answer:
In Schenck v. United States, Justice Holmes used the 'clear and present danger' doctrine to limit free speech if it endangers national security or others' safety.
Explanation:
In the case of Schenck v. United States, Supreme Court Justice Oliver Wendell Holmes used the expression 'clear and present danger' to characterize public dissent during wartime. This doctrine held that speech is not protected by the First Amendment if it poses a clear threat to national security or the lives of others. The case involved socialists distributing flyers discouraging men from joining the army during World War I.
Learn more about Freedom of speech limitations during wartime here:
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