Well, there was the attempted coup attempt in 1991, barely some six years after Gorbachev started his reforms. In contrast, Khrushchev's ouster from power came about ten years (1964) after his rising to the fore of Soviet leadership after Stalin's death. On a deeper level, the two leaders lived in very different political contexts. In the case of Khrushchev, the domestic failures of economic reform and his erratic behavior on the foreign stage (the CIA speculated he was a functional bipolar) gave his opponents a pretext to remove him. His opponents, led by Brezhnev, proceeded to lead the USSR into a period of economic stagnation and cemented a leadership caste. The problem with closing off a political system is that it cannot arrest the passage of time, and the Soviet leadership became increasingly older and in some cases, senile, as the seventies malaise drew on. The collapse of oil prices in the eighties eliminated one of the sources of foreign capital that kept the Brezhnev economy afloat. Foreign policy disasters like the Afghanistan quagmire and setbacks like "losing" Egypt after Camp David, US-Chinese detente, and the emergence of Solidarity in Poland added to a discrediting of the Brezhnev era and its hardliners. Thus when Gorbachev launched his twin policies of Perestroika and Glasnost, he enjoyed a great deal of legitimacy within both the Soviet public and large sectors of the Soviet bureaucratic state led by "young turks" whose careers had stalled because of the Brezhnev gerontocracy. There was an early political consensus that Gorbachev's reforms were vital to righting the foundering Soviet ship of state. Gorbachev's popular reception in foreign countries added a further sheen of legitimacy to him. Only when the reforms unleashed the centrifugal forces latent within Soviet society and undercut Soviet power did the hardliners within the USSR feel that not only should they act, but that they also possessed the legitimacy to overthrow Gorbachev through a public military coup. They were wrong on both counts, but Gorbachev's reforms did him no favors either, and he became a victim of the forces he unleashed as well.

The best short book on the Gorbachev period is the book Armageddon Averted by Steven Kotkin which introduces the concept that the Soviet system was "boobytrapped with idealism" and Gorbachev stepped on it.