In the 1918 case of Schenck v. United States, Charles T. Schenck and Elizabeth Baer were convicted under the Espionage Act for distributing leaflets that criticized American involvement in World War I and encouraged men to resist conscription. They appealed their convictions on the grounds that they violated their First Amendment rights to freedom of speech. The Supreme Court unanimously upheld their convictions, with Justice Oliver Wendell Holmes Jr., writing for the court, introducing what became known as "clear and present danger" test: whether 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 substantive evils Congress has right to prevent is a question of proximity & degree. In this case, during wartime when recruitment was necessary for national interest, discouraging enlistment posed an immediate threat justifying restriction on free speech.

In the dissenting opinion for Schenck v. United States, Justice Oliver Wendell Holmes Jr. argued that the First Amendment's protection of free speech should not be curtailed unless there is a clear and present danger that will bring about substantive evils Congress has a right to prevent. He believed that Charles Schenck’s distribution of anti-draft leaflets during World War I did not pose such a threat, as it was merely an expression of his political beliefs rather than an incitement to lawless action. Holmes also criticized the majority's reliance on English common law precedents which he felt were irrelevant in interpreting American constitutional rights. Furthermore, he contended that even if some recipients of Schenck’s leaflets might have been influenced to resist conscription, this potential effect was too indirect and uncertain to justify suppressing his freedom of speech.