Russia at present is an autocracy layered over an oligarchy.
Putin has been very effective at consolidating power by virtue of enabling those below him to enrich themselves.
This has been an effective strategy.
A difficulty is if you are percieved to disagree with him. Those who find themselves in this position have found themselves deprived of at least one of the following: wealth, liberty, life.
Can he continue?
My read is he is already on borrowed time.
While US presidents come and go at the electorate's nominal whim, Russia's premier has tied himself to the control he exerts.
When that diminishes, he goes.
If Putin is replaced it will be be someone more aggressive and brutal.
The main opposition in Russia is from Putin's right. Almost all those on his left have left.
The US also prosecutes political opponents on trumped up charges and persecutes those who disagree with the establishment line.
Russia is just more obvious about it.