[2] The radical Abern staunchly opposed World War I and following American entry into that conflict he refused induction into the military on political grounds.

In November 1920, the US Department of Justice attempted to make Abern a test case for the deportation of alien radicals citing Communist Party membership as sole grounds for action.

[2] Abern also briefly was part of a three-person Secretariat running the Young Workers League in the summer and fall of 1924 before being replaced as National Secretary on October 15 by John Williamson.

In 1925 Cannon became the National Secretary of International Labor Defense, the legal defense arm of the American Communist movement, Abern joined him as assistant national secretary and thereafter dedicated most of his effort in an attempt to build the size and influence of that parallel mass organization of the Workers (Communist) Party.

In that year he and other Trotskyists entered the Socialist Party en masse as part of the so-called "French Turn" tactic, a brief interlude ending with their expulsion late in 1937.

In accordance with these instructions, the National Committee suspended Burnham, Shachtman, and Abern at its meeting of April 22, 1940, giving the members of this so-called "petty-bourgeois opposition" an opportunity to recant and return to the party.

Burnham left the radical movement at this time, while Abern joined Max Shachtman's in establishing a new organization called the Workers Party of the United States (WPUS).

[8] Abern was elected to the governing National Committee of the WPUS at the time of its formation in 1940 and remained in the top leadership of that organization for the rest of his life.