about 15%~ of Biden's votes were by younger voters, who are more likely to be strongly against genocide, and much better informed about the conflict. They don't even need to be against Biden, just lose their enthusiasm for voting at the level they did in 2020. The Mulsim populations in swing states have been mentioned already.
I don't think it's a guarantee that it will cause him to lose, but it's naive to say it won't effect his chances. Things are going to be different when people are staring down the barrel of another potential Trump term, so I think he still has tons of time to pivot, but he's not going to shake this genocide Joe image, probably ever. As time goes on, it will be what more and more people remember him for in the way that people remember Obama for drone strikes.