And in order for that to happen, Democrats need to be a party that young progressive people are willing to be part of.
Which for a lot of them, means not fucking supporting a genocide.
Here's the thing. Republicans are fucked on this issue. They're always going to be fucked, nothing will change them, so it's a waste of time putting any effort besides discouraging support for them. Any half reasonable person already won't support them, so even that's of limited use.
Democrats, on the other hand, there's a chance. That's why it's actually worthwhile to call them out, to encourage pressure on them, etc. Even more so if third party is unrealistic, because that's the only way forward, so it first needs to become something that the people who'll take it forward are willing to be involved with.
Or, I guess, you can just sit back, whine "but Trump", and pretend the problems will just magically disappear if you get the current status quo Democrats back into office enough times in a row (assuming Palestine even still exists beyond the first term or two of this approach).
The Democrats won't learn shit if Trump wins because the party will be banished and all the young people who oppose the GOP will fucked for the rest of their lives.
I will always "but Trump" because defeating the GOP is the only thing that matters for this election. If Biden or whatever ham sandwich running opposes to him isn't equally as bad or worse, then further details don't matter.