In the biennio rosso of 1920–21, the richest period of political and social tensions, Damen worked first in Bologna with the local Trade Union Council and then with the Casa del Popolo ("House of the People") of Granarolo as the secretary of the Community Legal Committee.

In the months immediately preceding the split of Livorno he worked as secretary of the Trade Union Council in Pistoia and as the chief editor of the periodical L'avvenire.

On May 10 while returning from a rally held on behalf of the candidate of the Communist Party of Italy in the elections in the village of Corbezzi, he was detained by the fascists who took him to their offices in the city.

He was sent to Dumini with the proposal: "You should disappear for the entire period of the electoral campaign or hide yourself in a villa in Fiesole or remain in Florence under continual surveillance."

Renewing contacts with the party and overcoming the reserve of the comrades, he decided to return to Pistoia where he remained in order to continue the task of agitation.

On the return trip, made by car under the escort of a certain number of armed comrades, he encountered a squadron of fascists on the road from Pioppo to Caiano.

Bordiga, who enjoyed widespread support within the party, initiated his "Aventine" cession (named from a famous plebeian revolt in ancient Rome 4th century BC).

He attended the meeting of the central committee but did not intervene in the debate, thus not obstructing the change in political direction that was supported by Antonio Gramsci and Palmiro Togliatti.

In November 1926, Damen was imprisoned in Ustica, while in December of the same year he was arrested and sent again to the Murate in Florence for participating in the action of Florentine communists in plotting against the state.

Released under amnesty at the end of 1933, he was sent to Milan under watch for 5 years, while the head of the prison in Pianosa communicated to the Casellaria Centrale that "the punishment he has suffered has had no moral effect" and described him as an "unshakeable communist".