So, having a Jewish great-grandfather makes one half Jewish?
well Kerry's brother says that he and lurch are 50% jewish not a 25%.
And so do other news sources.
The Kerry brothers own Jewish background their paternal grandparents were born Jewish in the former Austro-Hungarian empire
http://jewish.com/modules.php?name=News&file=article&sid=1185
http://www.wmtw.com/Global/story.asp?S=1689357
http://www.nationalvanguard.org/printer.php?id=2041