The ONLY thing keeping Russia from steamrolling all of Europe at this point is their horrifically dire financial situation (thanks Mr.Reagan!). Their little incursion of Poland was cut short due to just that.
But if they amassed enough forces and pulled a serious tank blitzkrieg like the Nazis I imagine that they would overrun a fair amount of territory before the nations with any real amount of nuclear arms (namely England and France) managed to pull their heads out of their own arses let alone get the birds ready to fly in time for more than a Mexican standoff.
Sure Russia could overrun the Baltic states in 60 hours.
But don’t worry !
Obama and Ben Rhodes have this covered.