If Russia built bases next to them then you'd hear the same threats. And that was my point from the beginning.
I do see your point that the US wouldn´t have liked having Russian or Chinese troops along their Canadian or Mexican borders.
But I saw the recent CNN interview with the NATO secretary general. Ukraine actually applied for NATO membership back in 2008, he wouldn´t answer why they were never let in all these years. In others words NATO been scared of Putin all along, and Ukraine were never going to get in anyways. So I don´t quite see Putin´s NATO argument here.
Also, what are the benefits here from Putin´s point of view (I´m not suggesting you support him, just to get an understanding)? Even if he inserts a puppet regime he´ll be stuck with sanctions and damaged political relationships which will harm the Russian people.
And Yanukovych was a Putin puppet and the Ukrainian people got rid of him so I don´t see how a new regime would survive either.