Uh.. no. Because they are idiots and terrible at working together. As strategically talented as the Russians are, their capability sucks because of their Achilles heel.
You can be sure that had they invaded with the right strategy, they would have taken Kiev from the outset and the rest of Ukraine would have fallen. No one would have moved to help. It was only once they showed how utterly incompetent they were that the US defense mafia decided they could kill Ivans for cheap and make oodles of money for themselves with relatively little risk.
All it takes is a million dead Ukrainians (by the end of this) and risking a nuclear war. I mean, whats the big deal?