In this article, I examine the power struggle inside the Chilean Communist Party's inner circle during the mid 1940s. I document the attacks of Galo González, Humberto Abarca and Ricardo Fonseca against the General Secretary, Carlos Contreras Labarca and I argue that Ricardo Fonseca eventually ended up replacing Carlos Contreras as the General Secretary because he managed to get the support of some key Chilean Communists and some important leaders of the international Communist movement. These events led to a significant turn to the left, which hindered the continuation of the historical alliance with the Radical Party. My investigation is based mainly on reports made by the United States' Federal Bureau of Investigation (FBI).