Large numbers of Eastern European Ashkenazi Jews were seduced by Communism because it was the enemy of the Czarist Russia under which they had suffered for so long. You won't find the same infatuation with Communism among Sephardic Jews.
They followed the philosophy of, "The enemy of my enemy is my friend."
Unfortunately, this love affair with Communism was brought to America by late 19th Century and early 20th Century Jewish immigrants before they had a chance to see for themselves what a horror Communism was. Throughout the 20th Century, the children and grandchildren of many of these early Ashkenazi Jewish immigrants were raised as "Red Diaper Babies" without questioning whether Grandpa's love of Bolshevism in the 1910's was justified.
The "Red Diaper" Jewish generations are now dying off from old age. The new Ashkenazi Jewish generations are seeing for themselves that the Left has embraced the new enemies of America which also happen to be the enemies of the Jews.
Following the "The enemy of my enemy is my friend" phenomenon, I see the younger Jewish generations leaving Grandpa's Bolshevism behind and coming over the to Republican Party.
About the changing Jewish vote --
I'm reminded of a clever "New Yorker" cartoon I once saw.
Two men sitting in lounge chairs on the beach. One says to the other: "They say Castro's days are numbered. Unfortunately, it appears to be a rather high number."