It's an incredibly difficult thing to do, and it can't come from the outside. Russians have to collectively decide that they don't accept the situation anymore, and that they're prepared to pay the price with their blood. They did in 1918, and I wish I could support them to do it again.
Of course it's easier said than done. And yet I'm not claiming that it's easy, quite the opposite.
That's not true. The President of Ukraine who was overthrown in 2014 (Yanukovych) was democratically elected in 2010 in an election that international observers called fair, truly competitive, and an impressive display of democracy.[1]
That President was supported mostly by the people of eastern Ukraine and opposed by the people of western Ukraine.
1: https://www.theguardian.com/world/2010/feb/08/viktor-yanukov...
So was Nazi Germany. Everyone there still had to accept thorough "de-Nazification" after WW2, though.
(This makes it doubly ironic how exactly that is what Putler claims to be doing to Ukraine.)
Russia is a non-democratic country...