That is total, absolute, nonsense.
The Jewish vote was the same before Roosevelt, and WWII.
Well, my personal observations don't go back as far as pre-WWII, and my sample space is small. But, I don't think it's nonsense for those I observed.
Curiously, and supporting your view, I've heard that a good number of Russian Bolshevik revolutionaries were Jewish, until Stalin cleaned house.