The essential militant forces of the PSoL come mainly from the political current Movimento de Esquerda Socialista (MES, Movement of the Socialist Left) and Corrente Socialista dos Trabalhadores (CST, Socialist Current of Workers). These two organizations are part of the tradition of Morenist Trotskyism. They remained in the PT, still united, as the CST, when the then majority of Socialist Convergence formed the Socialist Party of United Workers (PSTU).
Former militants and leaders of the PSTU, like Junia Gouvęa and Martiniano Cavalcante, who left this party at different times, are part of the leadership of the PSoL. A small group of militants, who have not respected the decisions of the National Conference of the Socialist Democracy Tendency (DS), are grouped in “Liberdade Vermelha” (“Red Liberty”) and have come out in favour of the PSoL. They have not submitted this decision to any collective debate inside the DS.
Milton Temer and Carlos Nelson Coutinho - who taught us Gramsci and the concept of process in the revolution - are also inside this new party, as well as Francisco de Oliveira.
The disenchantment provoked by the Calmar government and discontent at the evolution of the PT can lead different political traditions to come together and proclaim a new party. But in the light of the experience of the PT, we know that to build a useful political tool much more is needed. And we are not talking about the 438,000 signatures needed to get onto the electoral register  but of the absence of a reasonably “warm” social and political environment capable of merging different conceptions in a common programme to produce a transformative political action.
The 7th National Conference of DS in November 2003, approved the following resolution:
“We consider the pursuit of the defence of the positive values originating in the history of the PT valuable (the programmatic contribution; rights of tendency and internal democracy; feminist conquests; the synthesis of the experiences and the forces of the left). In this framework it is also necessary to renew the links between the partisan organization and the broad political-social movement around the PT.
“We seek to intervene in the battle of orientation inside the PT, basing ourselves on the legitimacy of the defence of the historic and strategic project of a socialist and democratic party. Faced with the development of a conflict inside the party, it is more than ever necessary to put forward the construction of a broad left current which is the pole of reference of the reconstruction and functioning of the PT as a socialist and democratic party.
“The construction of this current and the struggle for the socialist reconstruction of the PT represent an alternative also faced with the sharp pressures seeking the abandonment of its programmatic character, that face those who wish to leave the PT and orient towards a project of a sectarian party, for these two orientations renounce the experience of the construction of a mass socialist and democratic party”.