Edit: I should add that Democrats often rely heavily on mobilising the youth vote. The polling of under-30 voters shows a heavy majority who have sympathy the the plight of Palestine, and this is going to kill Biden. The Genocide Joe moniker is going to stick.
Most.. if not all... of them know it would be worse for the Palestinians with Trump as President vs Biden.
A lot of people won't be voting for Biden.. they'll be voting against Trump.