My feeling is that Clinton’s big problem was that she had a low ceiling and low floor because of 20+ years of smears; even though she was definitely qualified, there was just too much generalized negative baggage. I knew many democrats that believed something big would come out because republican muckrakers had spent so many years seeding that field. When Comey decided to break all tradition over nothing it just reinforced that perception.
Harris doesn’t have that, she has a high ceiling for perception. More people have no idea who she is and the more she can be the one to define herself while Trump looks crazier and crazier the better she’ll do. And the debate feeds that unlike Clinton.