Reagan called up Israel one night and told them to stop their assault on Lebanon. Israel stopped in less than 24 hours.
HW Bush called up Israel and ended that conflict overnight.
What makes you think Biden does not have the same power?
And if a phone call doesn't work, he could stop sending bombs. He could stop providing political cover. Instead of handing Israel billions of taxpayer dollars, he could impose economic sanctions like we did to Russia.
Joe Biden could turn Israel into a militarily vulnerable pariah state. What makes you think that this isn't enough leverage to end the genocide?