I wonder if the exit polls understate the Jewish population in the so-called “red states”, leading to an overestimate of their support for DemocRATS?
I think you are touching on a very significant factor there. Almost all this polling is done by left-leaning organizations. They probably extrapolate nationally from just a few big city 'rat strongholds. It's a lot cheaper that way, but scientifically sloppy. And I'm pretty sure, because of cultural differences, they would underweigh Orthodox and recent Russian Jews in their sampling, both of which have tended to vote GOP in recent presidential elections.
But remember what I said in post #1: the posted survey is of self-selected respondents and shouldn't be thought of as a poll.
Actually the exit polls don't attempt to count them in many states. CNN has a good database, they all use the same exit polls. If you review state by state results by religion, you'll note that Jewish only appears in the northeast and Florida. Most states, even states like Illinois and California and New York, are statistly insignificant. With the exception of Florida, in those states where the Jewish vote is recorded, it isn't much different that the general population.