I would like to add one additional point to the items listed in Anixx answer.
Russia is a federation where the balance of power is currently shifted towards the central government, yet there are regional elites that have their interests that might not entirely agree with the central government. The public support for the president is one of the few remaining cornerstones of the legitimacy of the central government in the regions when the budget transfers are dwindling and oil revenues decreasing.
Note that in the past few years central government also used criminal prosecution of regional governors to keep them in line, however this method is clearly unreliable when it becomes the only remaining one. The lower the poll numbers, the more bargaining power in the hands of regional elites.
In his 1999 essay "World Without Russia?" Thomas Graham identifies a pattern of constant struggle between the forces of decentralization and recentralization in Russian history. In 2000 the recentralization trend won. Apparently now this essay is becoming important (and oft quoted) again as Russia is approaching another historical junction.
Centralization often wins when there is an external threat and this is precisely what is being hastily manufactured by the central government. On the other hand decentralization is the only path to sustainable growth.
Yet it remains to be seen if this time around the regions would be able to build a sustainable federation.