A couple thoughts on the debate question about extending U.S. security guarantees to Israel in light of Iran's nuclear development:
1) Since when did George Stephanopolous start taking cues from Charles Krauthammer? (Cf. the link and comment thread for an interesting discussion of Krauthammer's position on deterrence and Israel.)
2) It's not clear whether Hillary's answer--that Iran needs to understand "an attack on Israel will incur massive retaliation"--is a Clintonian parse. It sounds to me like she's leaving herself room to insist it's Israel that will definitely retaliate, not necessarily the U.S. on Israel's behalf. If that's the case, Clinton is proposing that we maintain our current policy of strategic ambiguity in case of an attack on Israel. This was Obama's position as well.
That said, everyone knows America will coordinate with Israel, to an extent, if Iran attacks. The problem is that nobody can predict the exact circumstances of such an event, so it might be a bad idea to commit fully to a joint response now. One could easily imagine a situation where America and Israel are better off responding separately, maintaining a degree of public distance from one another. In that case, neither of us would appreciate being bound by the Krauthammer-Stephanopolous Doctrine.
3) Her point about extending deterrence to our Arab allies, however, is an innovation--albeit one that's been bandied about among think-tank types for quite some time (Expect op-eds. Many op-eds.). At first glance, it's a smart way to avoid charges that we favor Israel over our Muslim allies. It's also a logical extension of the current Bush policy--which seeks to "contain" Iran on the Cold War model, turning the U.S. into a guarantor of Sunni Arab security. And it's a first stab at preventing a proliferation domino effect whereby Turkey, Egypt, Saudi Arabia, etc., get nukes to defend themselves against Iran.
That said, I doubt Hillary has the details of this policy worked out in much depth, and they're probably where the devil resides. I've never seen a defense of a mideast security guarantee that isn't riddled with caveats, and--as this piece points out--many of the problems that frustrate Bush's attempt to contain Iran will also complicate Hillary's new policy as well.
*While I don't think Stephanopolous specifically asked about nuclear retaliation, it's Iran's nuclear program that prompted us to consider this guarantee. Thus, a nuclear conflict is at some level implicit.