The specious libel, about FDR being a Jew and that his name was really Rosenfeld, or even Rosenberg or some such, was begun in the late 1930s, when he had Jews on his team and nominated others for high office and judgeships. It was also said about him by Isolationists, America Firsters, and those who belonged to the American Bund, when he wanted to help England, before we got into WW II.
Nobody, NOBODY in the public knew that John Kerry's paternal grandparents had been Jews, who had CONVERTED, NOT JUST ATTENDE#D CHURCH, until he ran for president.
I'm not trying to disparage or insult you and/or your father; however, to be blunt, your father is ill informed and has told you spurious filth. Does he also believe that THE PROTOCOLS OF THE ELDERS OF ZION is a factual book?