The Minneapolis defendants were the first Americans tried under the Smith Act of 1940 — charged with conspiring to advocate the government's overthrow, on the evidence of their books, resolutions, and classes on Marxism. James P. Cannon's testimony, published as Socialism on Trial, turned the courtroom into a school; in December 1941, days after Pearl Harbor, eighteen were convicted of the advocacy count and sentenced to twelve to sixteen months.
The Communist Party publicly cheered the prosecution of its Trotskyist rivals — a position it bitterly regretted when the same statute was turned on its own leadership at Foley Square in 1949. The Supreme Court refused review, and the eighteen — Cannon, Dobbs, Vincent Dunne, Carl Skoglund, Grace Carlson, and their comrades — entered Sandstone and other prisons on New Year's Eve 1943, serving through 1944–45 as the war's clearest prisoners of conscience on the left.