 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.