The only obvious explanations is they are either stupid or insane.
I have to go with stupid: American Jews have had a love affair with communism since the Soviets destroyed the Nazis during WWII...even though the Soviets were as anti-semitic as the Nazis (or nearly so). They've maintained their love for the far, far left all these years (generations even)...even though the communists and the nazis aren't different in any significant way. So, in my mind, stupid it is.
I don’t know, but I’d surmise it’s the same as about every other victim group - Dems played on their fears starting long ago, and convinced them that Republicans are evil racists. Add to that, for Jews, equating “right-wing” with “NAZI” (as “opposed” to left-wing commie liberal Dem, which it ISN’T) and perhaps you have the nail in the coffin.