This article analyzes opinion polls conducted by the Brazilian Institute of Public Opinion and Statistics (IBOPE) in the context of 1964, with the objective of assessing the support to the coup and to dictatorship. The data, mostly new, indicate a contrast between the support to João Goulart, registered before the coup, and after the success of the coup, which points out to the good acceptance of authoritarian measures, including political purges. The empirical data obtained from the polls are used to consider the sources of legitimation of dictatorship that especially mobilized anticommunist representations. The analysis of the records suggests that the support to the authoritarian regime was marked by instability and oscillated throughout the initial years.