Gordon served as U.S. Ambassador to Brazil (1961–66), where he played a major role for the support of the opposition against the government of President João Goulart and during the 1964 Brazilian coup d'état. On March 27, 1964, he wrote a top secret cable to the US government, urging it to support the coup of Humberto de Alencar Castelo Branco with a "clandestine delivery of arms" and shipments of gas and oil, to possibly be supplemented by CIA covert operations. Gordon believed that Goulart, wanting to "seize dictatorial power", was working with the Brazilian Communist Party. Gordon wrote: "If our influence is to be brought to bear to help avert a major disaster here--which might make Brazil the China of the 1960s--this is where both I and all my senior advisors believe our support should be placed."