I recently exchanged views with a Harvard educated Jewish friend on Jewish Americans' political leaning. This is what she has to say (I have her permission to share her view): "Most Jewish-Americans are socially liberal. Jews have 3 main types of temples. The Orthodox are super-traditional. The Reform Jews are the most assimilated. Those are smaller groups. The most popular temple, the Conservatives, are in the middle. With the exception of the Orthodox, Jews are raised to be social liberals.
Jews have been persecuted for thousands of years, all around the world. That history causes most Jews (at least those who are familiar with that history, which is most) to have a natural affinity for the underdogs. The Republican party’s consistent support of Israel is a small counter-point, but most US Jews (or partial Jews) today are less concerned about Israel than other issues.
This could change. Most Jewish kids are now marrying non-Jews, which exposes them to a wider range of views on all sorts of issues. And after being part of the upper-middle class for three generations, I also think that some Jews are becoming more fiscally conservative. Some also have become increasingly aware that decades of Jewish support for inner city minority communities have not led to mutual support.
Even as Jews become more moderate on a range of issues and could potentially be persuaded to vote for Republican candidates, the Republican party sometimes endorses social conservatives who make most Jews feel very uncomfortable. E.g., it is difficult for anyone with a Jewish background (perhaps other than the Orthodox Jews) to support someone like xxxxxx (redacted)." I think this explains why most American Jews (except the Orthodox Jews who are a tiny minority) have voted for democrats. The reason, simply put, is they identify with democratic core values.