In 1924 Amendola refused to adhere to the "Listone Mussolini", and attempted to become Prime Minister, at the head of a liberal coalition which ran in the elections.

The document directly implicated Prime Minister Mussolini in the murder of Giacomo Matteotti, the leader of the Socialist PSU party, on the 10 June 1924.

Resented by Mussolini for his prominent activism, Amendola was, together with the Unitary Socialist Party deputy Giacomo Matteotti and the popular priest Don Giovanni Minzoni, one of the régime's earliest victims, as he was beaten by 15 Blackshirts with clubs in July, 1925.

Amendola formulated the notion of totalitarianism as total political power which is exercised by the state in 1923, describing Italian Fascism as a system which was fundamentally different from conventional dictatorships.

[4] The term was later assigned a positive meaning in the writings of Giovanni Gentile, Italy's most prominent philosopher and leading theorist of fascism.