Presenting the sitting vice president of an unpopular administration as “the change candidate” was audacious. As Noah Rothman writes today, it may not have been a sustainable strategy even over the course of a relatively short campaign.
One problem with it: Her candidacy required that Biden fade far into the background — there are of course other reasons for that — and that she be packaged as a major decision-maker in the administration. That left her as the Democrat we most frequently see in the news. With modern media cycles and attention spans being what they are, the novelty of Harris as the nominee has disappeared. By the time most people vote, it will feel as though she has been running and in charge for a long time.
If Biden were a bigger presence in our politics, though, she would either be supporting him (and looking like neither a leader nor a change agent) or using him as a foil (breaking Democratic unity).
Another what-if: Say Biden had dropped out in mid 2023, and Harris had won a competitive primary to succeed him (perhaps with no endorsement from him until late in the process). She would then have had time to establish herself as loyal to Biden but different from him, and thus to present herself more credibly as an agent of change. Of course, an earlier Biden exit would have had several downsides for her — for one thing, she could have lost the primary.