Glaberman was associated with the Johnson-Forest Tendency, a radical left group which understood the Soviet Union as a state capitalist society that split from the Trotskyist Socialist Workers Party, which understood the Soviet Union as a degenerated workers' state.
In 1950, the Johnson-Forest Tendency left the Trotskyist movement and became known as the Correspondence Publishing Committee.
He was a major figure in the new group, Facing Reality, until he proposed its dissolution in 1970, over the objections of James, because Glaberman felt it was too tiny to operate effectively.
He was for many years, until his death, a sponsor of New Politics and served as an associate editor of Radical America, along with individuals such as Paul Buhle.
Documents, "reflect their many years of involvement in the labor, civil rights and women's movements.