Harris was out two months ago due to lack of money and not really being inspirational. She was perhaps the smartest person running, but campaigning is CHA-based, not INT. I suspect she could have gutted it out to Iowa and New Hampshire, after X weeks stuck in an impeachment trial, where people wouldn't care about her non-whiteness and lost there. But Kamala probably rolled an intelligence check high enough to realize that this wasn't her time, and to get out before she got damaged. Oppo research always finds something, because people make mistakes.
"Kitto daijoubu da yo." - Sakura Kinomoto