Any American “surprised” at internal Russian dissent must have been asleep when reviewing Civil war turmoil — Lincoln went thru half a dozen gen’rls before he found a drunkard willing to fight.
This is normal in a fight to the death, children.
Putin must worry about his “generals”, but the real government power in the Russian government comes from the intelligence apparatus.
However, the people who might kill Putin are the oligarchs who have lost billions of dollars in wealth (they blame Putin), fear the Russian people (look at Russian history), and make Machiavelli look like a piker. They have everything to lose to include their wealth even as most in the West believe Putin “made them”.
The looting of Russia by the upper crust of their society is massive and despite the historical perception of the Russian people as somber and accepting peasants there is a LOT of simmering resentment ripe for the picking by an ambitious populist figure.