These are the main reasons American Jews are Dems:
1. There have been 4 (perhaps 5) distinct waves of Jewish immigration to the US.
A) Mid 1800s, from Germany, capitalist, store owners, business men.
B) Late 1800s - WWI, mainly from Eastern Europe. Worked in the "sweat shops" of the Lower East Side and helped form the labor movement. Politically socialist.
C) Post WWI - pre WWII , also from Eastern Europe, but now including anyone who was getting the Nazi vibes. Those who didn't go to the US or Canada went to "Palestine" to work the land. Same socialist ideals as the earlier wave, they created the "kibbutz", the communal farm, where kids would eat and sleep separately from the parents. This was as close to pure Marxism as was ever created. It was successful only as long as everyone contributed equally and as long as the Arabs kept attacking. Israel's economy was run by the Labor party for decades with high union participation. It was only unleashed when Bibi became finance minister in the mid 1990s and he privatized many government services and deregulated. That's why Israel has so many NASDAQ listed companies.
D) Post - WWII. (notice that there was nothing during WWII, as the US and other countries made sure the Nazis had as many Jews available to slaughter as possible) These were destitute people who used to have businesses in Europe and started new ones in the US.
E) 1970s - 1990s, Soviet Block. These people lived the reality of communism that the emigrants of 80 years earlier idolized, but never endured. They are majority Republican and want nothing to do with the Dems.
So, which of these groups comprise the Dem (dumb) Jews? Primarily the ones from B and C, plus their kids and grandkids who vote Dem because mommy and daddy did. This is also the group of "progressives" who value their leftism more than their Judaism, even as their leftist brethren organize Gaza flotillas and Divest Israel campaigns. If they attend a synagogue, it's usually Reform, which has the most lenient observance standards. They will also be the most fervent ACLU members. They are most likely to sue communities to to remove Christian symbols from flags and memorials because they have so little connection to their own faith that they feel they must deny it to others as well.
Typical example: Paul Krugman.
"Krugman was born to a Jewish family,[11] the son of Anita and David Krugman (1924–2013). His paternal grandparents immigrated from Brest, Belarus, then Poland, to the United States in 1922."
Nothing there that I disagree with but I think it kind of skims over the specific question as to WHY most American Jews are liberals and thus Democrats.
I still believe, as I said in my original post, that the largest number of American Jews came to the US between about 1880 > 1920. His type “B”.
“Form the labor movement, politically socialist”. Yes.
They also MISSED the deadliest years of Stalinism. Jews were eagerly persecuted and harassed for hundreds of years in Czarist Russia, so they were happy to see (indeed, as you have pointed out, some Jews were the ideological leaders of) the Marxist Revolution circa 1917 and believed it to be the harbinger of better times. So what did they do? They started reading the NY Times in their new country with their newly-learned language as best they could and longed wistfully for Mother Russia.
We know how that worked out, but Russia, then having turned into Communist Russia, did so without them. They never got news about all the great stuff that was going on in the gulags (actually, very few did) but the NY Times was very effusive about these new industrial leaders in Europe and Russia who were making trains run on time and of course, improving the lot of common people everywhere within their borders.
So the “why” for me, is this happenstance of history; where agrarian people came to the New World, were forced to work in industry, and naturally became caught up in the unionization part of the general industrialization that was going on at the time. They longed for the nation of their births, believing that the revolution that had occurred there, without them, was bound to make things better for their people. Forget not that all these people were willing to give up all that was familiar (Czarist Russia, pure hell for them) to trade for their new lives. And if a few dozen million people were exterminated that those early 20th century American Jews didn’t especially know about, no big deal. So it is this residual “lore” that is passed down to present-day Jews all throughout their childhood.
The analog to present-day Hondurans and El Salvadoreans who come to the US is obvious, but I have no interest in wandering off into that topic.
So today, the question is, why do or how can Jews overlook blazingly obvious and many-times repeated evidence that the Arab world wants them destroyed; versus logically thinking through...”Hmm, four wars, three of which were near-existential, 2 intifadas, gave them back Gaza, 9000 rockets over the past year, OK, let’s feel sorry for them”.
It’s because that lore was implanted when they were children that it has the force it does over their thinking. They don’t apply logic nor rationality to their situation, they believe they are being loyal to their culture by honoring the traditions of their parents WHICH IS NOT observing the religion, it is repeating and identifying with the lore. Because they are lazy suburbanites. They identify with the underdog, no matter how much of a scumbag the underdog is, even when the underdog actually wants to kill THEM.
I should also add, that the final layer of liberal cement was laid in when those recent immigrants and their kin saw the depressions of 1907 and 1921 rapidly overcome, the boom boom times of 1925-1929 and then the emergence of FDR as the national father figure in the depths of the depression into WW2.
You forgot the original American Jews: Sefardim were the dominant group until perhaps the 1840s, and they were most numerous in the South.