McDermott nevertheless cautioned against "over-simplistic stereotypes"—promoted in the fiction of writers like Aleksandr Solzhenitsyn, Vasily Grossman, and Anatoly Rybakov—that portrayed Stalin as an omnipotent and omnipresent tyrant who controlled every aspect of Soviet life through repression and totalitarianism. Service similarly warned of the portrayal of Stalin as an "unimpeded despot", noting that "powerful though he was, his powers were not limitless", and his rule depended on his willingness to conserve the Soviet structure he had inherited. Kotkin observed that Stalin's ability to remain in power relied on him having a majority in the Politburo at all times. Khlevniuk noted that at various points, particularly when Stalin was old and frail, there were "periodic manifestations" in which the party oligarchy threatened his autocratic control. Stalin denied to foreign visitors that he was a dictator, stating that those who labelled him such did not understand the Soviet governance structure.