So let's put aside the massive, indeed unprecedented, arguably literally insane response from both the media and the Democrats (but I repeat myself) to Trump's electoral victory. Obviously such a temper tantrum will work up Democrat partisans and the media -- but I repeat myself again -- to a fever pitch of disapproval and disgust. That accounts for the 45% right there: they were stupid enough to vote for Hillary Clinton, so obviously they aren't happy.
What about the rest?
Well, 14% say "great" start, 21% say "good" start. That's 35%. That covers the portion of the Republican base that actually liked Trump. Add the 19% who said "fair" start and you get 54%.