The question was first addressed to Obama, and then to Clinton:
STEPHANOPOULOS: During the Cold War, it was the United States policy to extend deterrence to our NATO allies. An attack on Great Britain would be treated as if it were an attack on the United States.
Should it be U.S. policy now to treat on Iranian attack on Israel as if it were an attack against the United States?
CLINTON: Well, in fact, George, I think that we should be looking to create an umbrella of deterrence that goes much further than just Israel. Of course, I would make it clear to the Iranians that an attack on Israel would incur massive retaliation from the United States.
But I would do the same with other countries in the region. We are at a very dangerous point with Iran. The Bush policy has failed. Iran has not been deterred. They continue to try to not only obtain the fissile material for nuclear weapons, but they are intent upon using their efforts to intimidate the region and to have their way when it comes to the support of terrorism in Lebanon and elsewhere.
And I think that this is an opportunity, with skillful diplomacy, for the United States, to go to the region and enlist the region in a security agreement vis-a-vis Iran.
<snip>
And we will let the Iranians know, that, yes, an attack on Israel would trigger massive retaliation. But so would an attack on those countries that are willing to go under the security umbrella and forswear their own nuclear ambitions. And finally, we cannot permit Iran to become a nuclear weapons power. And this administration has failed in our efforts to convince the rest of the world that that is a danger, not only to us, and not just to Israel but to the region and beyond.
Therefore, we have not to have this process that reaches out beyond even who we would put under the security umbrella, to get the rest of the world on our side to try to impose the kind of sanctions and diplomatic efforts that might prevent this from occurring.
http://abcnews.go.com/Politics/DemocraticDebate/Story?id=4670271&page=3