You say Israel is a nuclear power, what might be only your supposition as it has never been confirmed by any Israeli government. Even being true it could not be used against Gaza or Lebanon or Israel would end like Gomorra did and not even Lot would be spared. We should not forget that unfortunately Israel is now a rogue state and this makes it difficult for the USA to keep protecting as they did until now. We should also not forget that oil does not have the same vital importance it had 75 years ago.