"If you really want to wreck Russia, what you should do is to encourage it to try to conquer Ukraine. Putin is much too smart to try to do that." John Mearsheimer, 2015.
Putin's argument that Nato was a threat is just a distraction. There's nothing Nato could do if Ukraine joined Nato that Nato couldn't already do without Ukraine.
Mearsheimer's argument that Russia should be left alone to violate the sovereignty of her neighbours is just bonkers. Thank goodness he was ignored.