They both grossly overestimate the effect that our actions have on Putin.
Mearsheimer blames us because we expanded NATO (which I agree was a horrible mistake, but do not agree it made war inevitable).
Conservative anti-Biden zealots blame us because somehow we were insufficiently strong during the 13 months of his presidency.
In both cases this is what psychologists call “centrality,” or the tendency to overestimate OUR effect on THEIR decisions. We are the center of our universe, so we assume we are the center of their’s, too.