Alfonsín bought a local newspaper ("El Imparcial"). He joined the Radical Civic Union (UCR) in 1946, as a member of the Intransigent Renewal Movement, a faction of the party that opposed the incorporation of the UCR into the Democratic Union coalition. He was appointed president of the party committee in Chascomús in 1951 and was elected to the city council in 1954. He was detained for a brief time, during the reaction of the government of Juan Perón to the bombing of Plaza de Mayo. The "Revolución Libertadora" ousted Perón from the national government; Alfonsín was again briefly detained and forced to leave his office in the city council. The UCR broke up into two parties: the Intransigent Radical Civic Union (UCRI), led by Arturo Frondizi, and the People's Radical Civic Union (UCRP), led by Ricardo Balbín and Crisólogo Larralde. Alfonsín did not like the split but opted to follow the UCRP.