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.
My parents were traditional Brooklyn liberal Democrats until my grandparents died. Then when Reagan came into office they became conservatives.
I think a lot of is was respect for that generation of European Jewish Socialists that came to America and got greeted in the new world by the Democrats/Communists.
The author is way off on that too, Obama only got 78% of the Jewish vote, Gore got 79%, and Clinton got 80%, the Jewish vote (since 1916) has been in the 80s for 5 times and hit 90% three times. Since 1916, Obama's total of the Jewish vote was exceeded 10 times and more if you count the combined anti-Republican vote, because Jews will vote in large numbers to the left of the Democat party if they can.
The Jewish, anti-Republican vote was already comfortably in the 70s by the time that pre-Hitler, and pre-war Roosevelt picked up his 82% in 1932.