had been expelled from political life. At this time, along with other intellectuals, he the leftist party, the Brazilian Democratic Movement (MDB), one of two political parties permitted by the militaries. Alongside Almino Affonso, Francisco Weffort and Fernando Henrique Cardoso, the party nurtured important leaders like Marcos Freire and Jarbas Vasconcelos. In parallel, Arruda Sampaio, Affonso and Weffort launched the candidacy of Cardoso for the Brazilian Senate. The agreement between them was to build a new left-of-centre party if Cardoso won more than one million votes (he received 1.6 million votes). The party already had a platform and would be called the People's Democratic Socialist Party (PSD). According to Arruda Sampaio, the new party would be democratic and mass-based popular program and socialist, organized in clusters. But the idea of creating a new party was aborted by Cardoso's change of plans. After being elected senator in 1978, he stated that the strengthening of the MDB party was a priority, despite the promise made to Arruda Sampaio, Affonso and Weffort to build a new party. Arruda Sampaio, perplexed by the reversal, broke from the MDB. Foundation and trajectory in the Workers' Party (1980–2005) Disappointed with the attitude of Cardoso, Arruda and Weffort entered the Workers' Party (PT) at its foundation, in 1980. Arruda was the author of the rules of the party and one of the creators of its core base. In 1982 he ran for congress for São Paulo and lost, but later he came to occupy the seat of Eduardo Suplicy, who resigned to run for mayor of São Paulo. In 1986, Arruda Sampaio was elected deputy of the constituent, with 63,899 votes, was the second most popular deputy of the PT (after Luiz Inacio Lula da Silva) and the 27th most popular in São Paulo. As a member of the constituent assembly, he became widely known for proposing and defending a model of constitutional reform which aimed to wipe out the plantations, and also became the only PT deputy to chair a working committee. During the constituent assembly, Arruda was a member of the drafting committee, the committee of systematization, the committee on state institutions, and the subcommittee on cities and regions which he presided. He was also deputy leader of the PT in 1987, and replaced Lula da Silva in the party leadership in 1988. At this same year he lost to Luiza Erundina the PT nomination