Two Theories on Why American Jews Still Vote Democratic
First, the two mysteriously persistent Democratic ethnic groups (blacks and Jews) were reliable Republican in the late 19th century. It might simply be a matter of “They won't fool us again.”
Second, according to this study (Exhibit 7 on page 27), only 13% of both religious Jews and agnostics of Jewish descent are Republicans but 40% of Jews who have converted to other religions are Republicans. They have been subjected to the propaganda campaign that there's something Jewish about modern liberalism and they have responded. This isn't even limited to the United States.