Jewishness (is that a word?) is only passed on by the mother. So Kerry claiming a grandfather was Jewish means nothing. When someone says (usually a disparate democrat politician)
Oh, see, I like bagels and cream cheese. I must be part Jewish!, they are feeding voters' desires to delude themselves into thinking up is down, day is night, and bondage is freedom. The voters, in this case overly reform Jewish urbanites, let themselves fall for this hook and happily go for the self delusion because they are terribly concerned about what other people think - those other "people" being the self appointed intelligentsia and media.
Thank God for the Founders' foresight in creating the Electoral College.