A historically vulnerable position? Vulnerable to what? To an invasion by NATO?
There's two ways you can answer that question. The first is, no, it's not vulnerable, because there are exactly zero NATO members who have any interest whatsoever in invading Russia. That is simply not going to happen.
The second answer is to remember history. Napoleon invaded and captured Moscow. Hitler invaded and made it to just outside Moscow. Both of them started from further west than NATO could start. So, yes, from the perspective of history, Russia has less of a geographic buffer than it had in the past.
But I think Putin isn't really afraid of a NATO invasion. What he's really afraid of is a color revolution. He therefore is building grievances against the West, not because he fears NATO, but because he fears real democracy. (Yes, I know, the democracy in the west has problems, and is less "real" than it should be. It's still miles ahead of what's happening in Russia, though. And Putin wants the situation in Russia to stay as it is.)