The right answer IMO.
This was written 8 years ago as a rebuttal to the Mearsheimer position and it's hard not to say the author got it completely right.
This was written a couple of days ago by a top Russian scholar, and I think it is spot on. In a nutshell:
"The problem with their [Mearsheimer's] argument is that it assumes that, had nato not expanded, Russia wouldn’t be the same or very likely close to what it is today. What we have today in Russia is not some kind of surprise. It’s not some kind of deviation from a historical pattern. Way before nato existed—in the nineteenth century—Russia looked like this: it had an autocrat. It had repression. It had militarism. It had suspicion of foreigners and the West. This is a Russia that we know, and it’s not a Russia that arrived yesterday or in the nineteen-nineties. It’s not a response to the actions of the West. There are internal processes in Russia that account for where we are today.
"I would even go further. I would say that nato expansion has put us in a better place to deal with this historical pattern in Russia that we’re seeing again today. Where would we be now if Poland or the Baltic states were not in nato? They would be in the same limbo, in the same world that Ukraine is in."
Well worth a full read. (edit - I see a video with the author was posted on this thread the other day).