 Complete the following phrase:  He remained a member of the latter organization for over fifty years. His role in the organization was both artistic and political, with exhibitions of the groups work as well as activism. His graphic arts production includes well-known posters such as the one celebrating the victory of the Allies over the Axis powers in World War II and one protesting the execution of the Rosenbergs in 1954, who were convicted of espionage. These and other works became classics of the Taller de Gráfica Popular. In 1954, Bracho wrote a letter on behalf of the Taller to Guatemalan president Arbenz, expressing solidarity against a 