The Politburo model is designed for a leader to build coalitions among factions. Putin has been very good at doing that, but then he has been very successful at all the things he has done until now. His ability to hold things together declines as trust in his abilities declines and various factions concerned about the consequences of remaining closely tied to a failing leader start to maneuver. Like Khrushchev, who was failing in economic and foreign policy, Putin could have his colleagues remove him.

It is difficult to know how a succession crisis would play out, given that the constitutional process of succession exists alongside the informal government Putin has created. From a democratic standpoint, Defense Minister Sergei Shoigu and Moscow Mayor Sergei Sobyanin are as popular as Putin is, and I suspect they both will become more popular in time. In a Soviet-style struggle, Chief of Staff Sergei Ivanov and Security Council Chief Nicolai Patryushev would be possible contenders. But there are others. Who, after all, expected the emergence of Mikhail Gorbachev?

Ultimately, politicians who miscalculate and mismanage tend not to survive. Putin miscalculated in Ukraine, failing to anticipate the fall of an ally, failing to respond effectively and then stumbling badly in trying to recoup. His management of the economy has not been exemplary of late either, to say the least. He has colleagues who believe they could do a better job, and now there are important people in Europe who would be glad to see him go. He must reverse this tide rapidly, or he may be replaced.