If Israel decides to go into an all out war with Iran or whoever, they will be on their own. Maybe Great Britain would help, but if the current administration is still in power, then the United States will stay out of it.
It's just like with the embassies attack. This administration has placed blame on a YouTube video and not on the those who murdered four Americans. I'm pretty sure President Obama thinks if we weren't friends with Israel, the United States wouldn't be in the mess we are in today. That's why President Obama does stupid things to piss off our allies.
If Isreal goes to war, not this tit for tat crap that happens between Isreal and whoever all the time, but full blown, all out war, they will be on their own. I would even bet that President Obama would even tell Israel that we got their back, then after Israel starts something, he would laugh as everyone around them opens a can of whoopass on them and invades.