A large majority of American Jews oppose Israeli government policy vis a vis the Palestinian conflict. The Democratic party aligns better with their views on Israel. It’s pretty simple really.
No amount of supporting Israel will make most American Jews vote Republican, because most of them want to support Israel less. Most, or at least a very large minority, probably even want America to support Israel even less than the mainstream of the Democratic Party does.
Yeah, Israel is embarrassing, like have grandparents from the Shettle still around.