Anaxagoras
Banned
Well, there was a really good alt-history movie about this called Red Morning or something. It happened in that movie, so seems legit to me.
Yeah, in the movie the Soviets sent "three whole army groups" across the Bering Strait. Assuming the minimum of two armies per army group, that's six entire armies!
Sending paratroopers to conquer Colorado was the realistic part of the plot.