The government's central blow against the Communist Party was the 1949 trial of its eleven-member national board at Foley Square in Manhattan — nine months before Judge Harold Medina, the longest federal criminal trial to that date. The charge was not espionage, sabotage, or any overt act, but conspiring to advocate the overthrow of the government: the evidence was the party's existence, its classics, and the testimony of FBI informants. All eleven, including general secretary Eugene Dennis, Henry Winston, and Gus Hall, were convicted; Medina then jailed the defense lawyers themselves for contempt, a warning to the bar that defending Communists carried its own price.

The Supreme Court upheld the convictions in Dennis v. United States (1951), with Justices Black and Douglas dissenting — Black predicting that "in calmer times" the decision would be seen for what it was. Four defendants forfeited bail and went underground; Robert Thompson, a decorated war hero, and Henry Winston, who went blind in prison after a tumor went untreated, paid most heavily. Winston, his sentence commuted in 1961, remarked: "They have robbed me of my sight, but not my vision."