Russia will need to break up into smaller pieces before it is palatable for nato to absorb. Too geographically big right now. USA cannot tolerate anyone else in nato being big in any way that rivals them.
Geographical size means nothing and isn't a challenge to the US, Russia's economy isn't that important to the global economy. The Russian economy is smaller than Canada's and Canada is not only a NATO member but also geographically large.
Smaller than Italy's. PPP works in their favor, to some degree, but outside of natural resources and low-end manufacturing they're mostly holding on to the shadow of the USSR. It's not really a place for innovation, and not a great place to do business unless you're willing to hemorrhage cash via bribes and bureaucracy.