• 1940 Smith Act made it illegal to advocate the overthrow of the US government; was used to prosecute Communist Party leaders for their revolutionary views
• In 1951 case Dennis v. United States, Supreme Court upheld Smith Act as constitutional; with communists conspiring against the government, it was appropriate for the government to restrict communists' speech

Terminiello and Bridges, both decided in the 1940s, set a high bar for government restriction of speech. As Black had said, the evil must be "extremely serious" and the imminence must be "extremely high." But the circumstance-by-circumstance emphasis within Holmes's approach did allow the Court to go the other direction in deciding some free speech cases. If the "substantive evil" threatened was great enough, if the danger threatened was "clear and present" enough, the Court could hold restrictions on speech justifiable. For example, during the 1950s the Court twice ruled the Smith Act constitutional. Passed in 1940 amid anxieties surrounding the outbreak of war in Europe, and popular after World War II among those who believed that the nation faced a threat from communism at home as well as abroad, the Smith Act made it illegal to advocate, verbally or in print, the "desirability, or propriety of overthrowing or destroying the government of the United States."⁴⁸

In 1951, in Dennis v. United States, the Court held that the law did not violate First Amendment rights. In reaching this decision the Court drew a distinction between teaching and advocacy, between harmless discussion and dangerous preparation. "If Government is aware that a group aiming at its overthrow is attempting to indoctrinate its members and to commit them to a course whereby they will strike when the leaders feel the circumstances permit, action by the Government is required."⁴⁹

In 1957, the Court fine-tuned its position on the Smith Act. In Yates v. United States, the Court ruled that for advocacy to be illegal it must aim at achieving concrete results. Advocacy of some action "as an abstract principle" did not rise to the level that justified government intervention. And this sort of abstract advocacy was protected even when "such advocacy or teaching is engaged in with evil intent," so long as it was "divorced from any effort to instigate action to that end."⁵⁰

Critics of these decisions argued that they betrayed Holmes's subtle legal reasoning; some found in these decisions thinking more like Justice Sanford's back in 1919, when he had argued that revolutionary words were inherently dangerous, and that a spark could easily grow into a conflagration. But others argued that the Court's rulings were consistent with Holmes's formulation of the clear and present danger test. After all, Holmes had insisted that words and rights had to be considered within their historical context, and for many Americans, the post-war threat of communism was as severe as that which had convinced Holmes that Schenck's conviction was appropriate in 1919.