The Brooklyn-born playwright and critic Lionel Abel, who cut his political teeth in left-wing circles in Greenwich Village in the 1930s, remarked in his memoirs that during the Depression years, New York City “went to Russia and spent most of the decade there.” Leaving aside Mr. Abel’s taste for the mordant, he had a point.

For a few decades — from the 1930s until Communism’s demise as an effective political force in the 1950s — New York City was the one place where American communists came close to enjoying the status of a mass movement. Party members could live in a milieu where co-workers, neighbors and the family dentist were fellow Communists; they bought life insurance policies (excellent value for money) from party-controlled fraternal organizations; they could even spend their evenings out in night clubs run by Communist sympathizers (like the ironically named Café Society on Sheridan Square in Greenwich Village, a showcase for up-and-coming black performers like Billie Holliday).

What became the Communist Party U.S.A. (its name varied in the early years) was founded in Chicago in 1919 and, following a period of underground organization, opened its national headquarters in that city in 1921. But the bulk of the movement’s members were in New York, and in 1927 Communist headquarters were shifted to a party-owned building in Manhattan, at 35 East 12th Street, two blocks south of Union Square. (The building still stands, although under new ownership, and in what has evolved into a considerably less proletarian neighborhood than in the old days.)

New York would remain the capital city of American Communism from then on. Leading communists, including such figures as William Z. Foster and Earl Browder, had their offices on the top floor of the 12th Street building; accordingly, within the movement, it became the custom to refer to party leadership as the “ninth floor.” (And, for some reason, even in non- and anti-Communist left-wing circles, “the party” was always understood to refer to the Communists, rather than any rival organizations.)