Ok so to summarize.

We both think his position on Israel is a shit position that imperils his election.

Few questions for you in good faith.

1. How many voters do you think he loses in the other position. There are a lot of democratic voters that do strongly support Israel and might be put off by him pulling support of denouncing them. They could stay at home or withhold donations also imperiling his chances of winning the election.
2. What do you mean by “if progressives are loud enough.” What does that loudness look like? In 2020 you had Warren with popular support and Sanders turning out 50k people to rallies, that’s pretty frightening to a candidate and could get them to make concessions to bring them into the fold. The democrats aren’t running a primary (in any meaningful way) so what does “being loud” look like. Is it just posting wherever you can, is it some direct action, a protest, a rally? What about it would be more successful than the student led protests we see on college campuses that don’t seem to be doing much to sway Biden or his inner circle?
3. What do you think about the possible negative effects of such action? Are you concerned at all that there is some non-zero number of people that would have voted for Biden but see enough negative content they decide to sit it out unable to stomach voting for him?

Honestly I wish I had your optimism that we could work towards making a substantial change here to the course of events. I find what’s happening reprehensible, monstrous even. I took part in the Iraq war protests, took a bus from Ohio to DC to march in what was at the time one of the largest protests. Got there and was pepper sprayed by Capitol police but stayed in the fight, organized protests in Columbus in support of Medicare for all. I still work in my local community to try to make things better, but I found that “being loud’ even being historically loud didn’t move the needle because the system they taught me in school about how America works and the reality of how America really works are so different. Our representatives spend more time dialing for dollars calling up and begging the donor class for donations than they do legislating.

That’s the perspective I come into this with, almost 30 years of being told to organize, protest, vote. That the pendulum would swing back. Go read some of the comments on any YouTube video covering campus protests, see how much glee the right takes from watching the police crack down on them. What should we do when the tools they tell you will lead to your freedom energize your opponents and leave the people that supposedly represent you unmoved?