Beginning shortly before the 1905 revolution he was a cadre in the Zionist Socialist Workers Party in Białystok, Łódź, Warsaw, Kiev and Odessa.
As editor he tried to steer the Freiheit into a more broad left direction and resisted pressures to make its content dogmatically communist.
[5] In August 1929 both Epstein and Moissaye Joseph Olgin, the new Freiheit editor were censured by the party for taking a pro-Yishuv stand in reporting on the out break of violence in Palestine.
Under party pressure the paper changed its analysis reporting the revolt as a national liberation movement against the British and their Zionist collaborators.
The Comintern was silent on what stance to take, so they decided to send a personal envoy to the sister party to co-ordinate strategy.
This was the final event which sealed his disillusionment with the party, though he had been having misgivings for a decade since the beginning of the Third Period and then the show trials in the late 1930s.
[12] When he came back to America he briefly joined the staff of The Forward, but was fired soon after because he wouldn't go before the Dies committee or write sensationalistic material about the Communist Party.
[14] There he wrote his two major books Jewish labor in U.S.A. and The Jew and communism, independently published through a "Trade Union Sponsoring Committee" which was partly funded by ILGWU.