Israel is on its own."
Israel will be lucky if that is all that Obama does. He is likely to interfere as much as possible on the side of the Islamists. He can let it be known that there will be no consequences for Egypt if it attacks or sends military assistance to Hamas. He can release additional aid to front line Muslim states that can be used against Israel. He can provide intelligence on Israel military moves to its enemies. He can push the UN to interefere, and on and on.
I would say he has already done all of that.