I really don't think that Israel is that big of an issue for many American Jews other then those who maybe have family ties to the country. It's tough for me to see American Jews trending towards the GOP given that it's tough to see them moving away from Trumpism in the future and I really can't see a Ted Cruz type winning much more then 20% max of the Jewish vote. I also don't think Jewish millennials are politically all that different from the rest of their generation.
They're trending towards the GOP because the Democratic Party wants Palestinian voters. How can they sit by and watch Palestinians get access to the platform?