In neither of the cases you listed was the US trying to reach them with a small force before the Russians did. (Although they probably should have.)

That is exactly my point - wherever the US has gone in my lifetime it has been with massive force with a slow buildup and in technicolor and quadraphonic sound. But it appears to be elementary strategy that if you can put a small force in charge of airstrips and communication centres it doesn't matter that the other guys can beat you with massive force. After all, the US still does not want to get into an actual shootout with Russian troops. So, while the US wonders about how to deliver a crippling blow, maybe Russia will simply take control of Donetsk or Kharkiv with a small force. And then you'll come back to tell us that the US is still superior in speed and stealth.

A society committed to the notion that government is always bad will have bad government. And it doesn't have to be that way. — Paul Krugman