After Posadas' departure, Moreno became the central leader of the International's Latin American Bureau.

When the Fourth International was reunified in 1963, his current helped to found the Revolutionary Workers Party in Argentina.

This group oriented around fighting for union rights and mass-based party building.

After the LTF was dissolved, The PST helped to form the Bolshevik Faction which left the International late in 1979, partly in opposition to the nature of the USFI's support for the FSLN's strategy and tactics in the revolution of Nicaragua.

In response to what they viewed as an undemocratic process and pro-capitalist orientation of the PT, they left and formed the United Socialist Workers' Party (PSTU) but were also part of the IWL disintegration after Moreno's death.