Hypothetical question:
If Russian and Chinese troops were staged in Mexico, Cuba etc. what would the US do?
It's much too simple to paint Russia as the only aggressor here. It doesn't justify beginning a war, but it explains why they feel threatened - and with good reason.
Both sides should make concessions. There is no good and evil here, the world is not that simple, even if stupid politicians and media want us to think that to make us afraid, angry, hateful and get votes.
And honestly, look at all the wars and interventions the US started the last 50 years. How did that thing go: Who lives in glass houses, shouldn't throw stones...