Biden is betting he loses more supporters if he doesn't defend Israel. I hope beyond hope that he's right, but I'm not so sure.
The larger problem is that Biden doesn't seem capable of nuance. This is a complex situation, and it would be cool to have a leader who can acknowledge that Israel has the right to exist, and has also gone too far in it's war on the Palestinian people.
There are no heroes in this story. Nobody occupies the moral highground. Innocent blood is being spilled, and the people suffering have no agency in the conflict. It's just politics and victims of political violence.