Short answers, pulled from the story.
The Communist Party USA was founded in 1919 as a breakaway from the Socialist Party of America's left wing. It formed in the wake of the Russian Revolution, and by August of that year it already claimed between 50,000 and 60,000 members.
The party initially opposed American involvement after Germany invaded Poland in September 1939, following Moscow's line during the Molotov-Ribbentrop Pact. It reversed course again after Hitler broke that pact and struck the Soviet Union on the 22nd of June 1941. From that point on, the party fervently backed the American war effort.
Yes, from 1959 to 1989 the Soviet Union subsidized the party directly, with payments growing from $75,000 in 1959 to $3 million by 1987. The funding ended after Gus Hall condemned Mikhail Gorbachev's reforms, and the 1989 cutoff triggered a financial crisis for the party.
The government prosecuted party leaders including Eugene Dennis and William Z. Foster under the Smith Act in 1949, and the Supreme Court upheld the verdict by a 6-2 vote in Dennis v. United States. By 1957 membership had fallen under 10,000, with roughly 1,500 of those remaining working as FBI informants.
The Communist Party USA claimed 20,000 members in 2026, up from 15,000 in 2023, 5,000 in 2017 and 2018, and 2,000 in 2011.
In July 2024, dissenting members broke away to form a rival group, the American Communist Party. They pointed to CPUSA support for Democrats and an alleged abandonment of Marxism-Leninism. Online commentators Haz Al-Din and Jackson Hinkle became its founding chairman and founding Plenary Committee member.