Lopez Rega exercised an allegedly Rasputin-like power and influence over Isabel Perón during her presidency, and used both this and his unique access to become the de facto political boss of Argentina.

According to his biography by Marcelo Larraquy (2002), he was a respectful, introverted boy, who had a library covering an entire wall and a special interest in spiritual topics (which would later turn into a passion for esotericism and occultism).

(Evidently, Rega's esotericism included the writings of Alice Bailey: "Also found in his [Rega's] home were 12 volumes by Alice Bailey on telepathy and Cosmic Fire..."[2]) Sent to Argentina by Perón, exiled in Spain since the 1955 "Revolución Libertadora" coup, she organized a meeting in the house of major Bernardo Alberte, Perón's delegate and sponsor of various left-wing Peronist movements, among which the CGT de los Argentinos, a labour union federation which, between 1968 and 1972, gathered opponents to a pact with Juan Carlos Onganía's dictatorship, and which had an important role in the 1969 Cordobazo insurrection.

On the following days, Mario Roberto Santucho, leader of the Guevarist Ejército Revolucionario del Pueblo (ERP), held a press conference during which he accused López Rega and Colonel José Manuel Osind] of the massacre.

After finding out about Perón's meeting with José Ignacio Rucci and other right-wing CGT leaders and also with the Army, Cámpora and his vice-president Vicente Solano Lima resigned.

All of Cámpora's followers were sacked from all government positions, and López Rega's son-in-law, Raúl Alberto Lastiri, also a member of P2, became interim president and organized the elections.

Besides Raúl Lastiri's interim presidency, López Rega's success in the expulsion of the left-wing Peronists from power was confirmed on 4 August 1973, during the National Congress of Perón's Justicialist Party, with the nomination of his protector Isabel as a candidate for the vice-presidency.

Troubled by the right-wing shift of Peronism and of the government, the Montoneros, a left-wing Peronist group, assassinated CGT's leader José Ignacio Rucci on 25 September 1973.

In 1975 his protégé Celestino Rodrigo, Minister of Economy, devalued the Argentine peso by 50%, causing massive economic havoc, inflation, loss of savings, and general hardship on the middle and lower classes (in particular, public employees and retirees).

On 24 March 1976, President Isabel Perón was deposed by the military Junta, which in turn organized the so-called "National Reorganization Process" and generalized the "Dirty War".