Russia has a long history of claiming some existential thread to itself, as a justification to attack neighboring countries.
Putin clearly read some history books and is playing the same game as previous Russian leaders.
The thing is, with nuclear weapons, any intervention by other countries might lead to nuclear war.
The only ones that can safely remove him and his gang from power is the Russian military.
Hopefully, many more Russian soldiers will die, to the point that the army loses all it's will to fight Ukraine, and turns on Putin.