I think Iran is very much aware of what we would do should they attack Israel, not to mention what the very capable Israelies would do as well. I don't know why Hillary had to make such a strong statement based on a hypothetical situation, other than it's her usual posturing to show she has as big a set of cajones as the other boys.
There really is something to be said for 'speaking softly and carrying a big stick'. I find it ironic that we are in a very similar situation as the Soviets, and we know how well that worked out for them, right?