The main focus of this study is to analyze the control of constitutionality of the Supremo Tribunal Federal in regard to the partisan political process, starting from the analysis of the ADIns (Direct Act of Unconstitutionality) n. 1.354, brought into court by the Partido Social Cristao – PSC, and the main action, n 1.351, demanded by the Partido Democratico Trabalhista – PDT e pelo Partido Comunista do Brasil – PC do B, aiming to hinder the validity of the clause of barrier, foreseen in article 13 of the Federal Law n. 9.096/95 – Law of the Political Parties. Both judgments had unanimous votings, although divergent decisions. Thus, in the judgment of the ADIn no 1.354, judged in 1996, it was rejected the declaration of unconstitutionality of the barrier clause. However, in December of 2006, the judgment of the main action, ADIn no 1.351, its granting was judged. In such a way, in order to evaluate the legal and politics implications of these decisions for the Brazilian democracy, two effect are investigated: the judicialization of the political process and the politicization of justice. The first one, basically, is characterized by the intervention of Supreme the political dispute from the judgment of the ADIn no 1.351-3, and the second one by the political factors that influenced the way as the Supremo Tribunal Federal decided and, for evidence, the cause of its divergent judgments, in the ADIn no 1.354 and 1.351. Finally, through this panorama, it is inquired the political impact of the STF in the definition of the rules of the democratic system, not only as the “guard of the Federal Constitution”, which implies a certain neutrality in its decisions, but also by the influence of convenient political matters, decurrent of the composition of the federal government and the National Congress. At last, it is concluded that both decisions of the Supremo, on distinct periods, 1996 and 2006, were instrumental, which means that they were taken according to the government political necessities to maintain or/and increase its governmental basis in specific situations.