Nicola Bombacci was an important PSI’s leader during the First World War and the biennio rosso (1919-1920). After his expulsion from the PCd’I, of which was one of the founders, he approached fascism and became one of the last supporters of it since he had been shooted by partisans and died in Como Lake, and had been exposed in Loreto Square beside to Mussolini. After a short historical mention of the Bombacci’s political life, these pages will analyse deeper the question of the passage from the left to fascism in interwar Italy, through the analyse of his political language. The method executed in order to analyse the question foresees the use of a biography by dates and the identification of the political interpretation’s categories, which permit to carry out a comparison between the social-communist and fascist period. In conclusions, the article proposes a thesis of interpretation: the political passion.