In the landmark Supreme Court case of Schenck v. United States (1919), Charles Schenck was convicted for distributing leaflets that urged resistance to the military draft during World War I. The case raised important questions regarding the limits of freedom of speech as protected by the First Amendment. The Supreme Court upheld Schenck's conviction, arguing that his speech presented a 'clear and present danger' to national security. Based on this context, which of the following statements best encapsulates the significance of this ruling in relation to freedom of speech?