Harding died in office. There was a lot of talk about what killed him. The official story is that it was a stroke (cerebral hemorrhage), but he had other health problems and a lot on his mind. There were rumors of foul play, but that's unlikely.
Harding was long rated the worst of presidents (along with US Grant) because of all the scandals. That's changed a bit -- the country didn't fall apart when he was in office; in fact things improved -- but it's hard to see him making it up into the average category, let alone good or great, because he made bad appointments and didn't supervise what was going on.