The US has notoriously bad spy craft when it comes to Russia. We spent literal decades believing they were an equal power, spending vast sums on defense to make sure we didn't fall behind. The government funded all sorts of "studies" but anyone who questioned the narrative got blackballed, and the people who kept getting that work just parroted back what the generals wanted to hear.
And then the iron curtain fell and the Berlin wall came down, and we saw the state of their military...and it was abysmal.
We are seeing the same thing with their basic war capabilities right now. Ukraine has been able to hold them off, more or less, for two years using mostly NATO cast off equipment and sunflower seeds.
There's a pretty good book that goes over a lot of this by Anne Jacobsen called The Pentagon's Brain.