What you are telling me is that in the HYPOTHETICAL case that Kerry would ask for Israeli citizenship based on his father's ancestry, they would deny it? I mean, they would deny it not because who he is, but because his mother was not Jewish? I know that following the mother's line follows Halacha law, but I doubt Hitler cared for such niceties! It's been the question for centuries: what is a Jew?
As a disclaimer, I don't care whether Kerry is Catholic of Jew. American Jews seem to only pay lip service to Israel... if they do, at all. Look at Rahm Emanuel!