I strongly believe that part of the reason Jews vote ~80% Democrat is due to declarations by some Christian conservatives that the US is a Christian nation. For parts of the Jewish community this is viewed as antisemitic and a prelude to excluding Jews from legal protection.
I understand your point. Not to overstate the obvious, but that 80% who bristle at the notion that America is a Christian nation, or at least was founded as a Christian nation, are simply factually wrong and living in some kind of logic-free zone. One could have a good debate on just what “Christian nation” means in this context, because the founding fathers did not want the nation per se to have any particular religion. But having said that, its whole culture, moral fabric, legal framework, work ethic and just about everything that made (make) it a great country stemmed from the Christianity of the founders. I don’t mind administering a little self pat on the back to say that one could add a good dose of Judeo to that Christian origin. I am sometimes amazed at how well versed the founders, as well as Lincoln’s generation were in the Old as well as the New Testament.