On "Red Monday," June 17, 1957, the Supreme Court in Yates v. United States reversed the California convictions, holding that the Smith Act reached only advocacy of concrete action, not abstract doctrine — a standard the government's book-based cases could not meet. Pending prosecutions collapsed across the country, and no new Smith Act advocacy case was ever brought.
The membership clause survived a last gasp: Junius Scales, a North Carolina textile-family heir who had led the Party in the Carolinas, was convicted for membership alone and entered prison in 1961 — by then having publicly quit the Party after 1956 — becoming the only American imprisoned under the clause. An extraordinary campaign spanning his prosecutor's own doubts won a commutation from President Kennedy in December 1962, closing the Smith Act era after some two decades and well over a hundred political convictions.