It seems a bit of a historical change - in the 19th century view it would be ok for the Russians to get pissed off with the US trying to steal their Ukrainian peasants and associated property. These days you're supposed to let sovereign democracies do their own thing even if they have smaller armies.
“These days” also apply to us and our allies and it is an unfortunate part of how things run.
Yes, until they make the mistake of democratically electing someone you don't like, at which point you send in the secret services to instigate violent regime change.
There's an entire wikipedia article dedicated to the US doing that all over the place:
https://en.wikipedia.org/wiki/United_States_involvement_in_r...
They sort of did that to my own country (Greece) where they supported a ridiculous military dictatorship (Junta), although I don't think they actively helped it to power. If you find my comments coloured by a certain antipathy towards US external policy, that may be one reason.