I remember reading somewhere that the communists in Russia had to start killing/imprisoning their early supporters once the supporters figured things out because they really had the power to sway public opinion and it would not be in favor of the regime, which could not or had no intention of delivering on their grand promises.
Given the lack of complete data, it is difficult for Western scholars to establish the total loss of life brought about by the Stalinist terror. Adam Ulam and others estimate that in the Soviet Union as a whole, about 500,000 were executed in 1937-39 and somewhere between 3 and 12 million were sent to labor camps.