Just like with Clinton, it probably wasn't just one thing, but a cumulation of poor, wishy-washy decisions. Saying she wouldn't do anything different from Biden pretty much tied her to the incumbent at a time when an anti-incumbency wave was sweeping the world. Stupid stunts like that skit where her VP talked about "White Guy Tacos" and having marketing like "White Dudes for Harris" were also horribly judged unforced errors. Then when she appeared on SNL before the election she came across as desperate and literally pleading for votes rather than confident.
As for the people and who refused to vote for anyone who doesn't chant "Death To Israel", screw them.
The terrorists have been targeting hospitals, airports and chain stores to maximize the fear and chaos.