He joined the Argentine Communist Party in 1923 and, in 1926, is a member of the organizing committee of the Argentine Workers Party.
It is in Buenos Aires where he meets Mika Feldman who is as dedicated to the internationalist cause as he is. They remain a couple until his death in 1936.
They leave for Berlin in 1932 to join the group "Wedding" directed by the Austrian Kurt Landau, where they witness the rise of the Nazi's.
In June 1933 they return to Paris, where he publishes articles for the journal Masses, under the pseudonym Juan Rustico.