Then she went on stage in that debate, and she said yeah, we need more fracking. That moment, all the grassroots energy simply died down. There was a very short lag, a few days maybe, when people still tried to convince themselves. Then nothing. Just endless "Trump is bad".
Yes, Trump is really bad. Trump is a catastrophe. But he hasn't gained voters compared to 2020. It would be very easy to beat him by mobilizing the same number of left-leaning people that came out to vote four years ago.
For some reason, millions of the US voters decided to stay home this time. Unfortunately, it's a recurring pattern around the globe: sane politicians try to appeal to the insane crowd on the other side. In the process, they start saying things that aren't in line with their own principles and promises. This translates into marginal gains at best, but at the cost of alienating many of the previously faithful followers.
Your core is not a faceless crowd. It's people, and people have their limits.