Ho-Hum...
This is such an easy toss... It is the work of Liberals, largely in the '60s and forward which have extended the "separation of Church and state" to the ground (ie all the way down to the individual).
Prior to that time, the so called "separation" was limited to the federal level (Congress shall make no law...). It was liberal federal judges acting by fiat, who removed the sovereign right of the states respectively wrt religious matters. It is not the gist of the founding fathers intentions, nor can you prove it to be so. The curtain of separation was meant to extend no further than the federal level.
Also, prior to that time, and reaching all the way into our very beginning, Blackstone's Law (influenced heavily by the Bible) and the Holy Bible itself were regularly used in law at all levels in our courts. No other holy book was given this regard.
Furthermore, prior to the 60's, with hardly an exception, all of the tested law was specifically regarding denominations with the odd Deist or Hebrew thrown in. IOW, prior to the '60s certainly prior to the 50's, States had full right to religious testing and law, School prayer, Sabbath laws and all, and the only tested law (AFAIR) was between Christian denominations, or at the least Jehovah-centric religions.
The only deference to religion other than Christianity ever given here historically was to our Hebrew brothers, and rightly so. Their God is our God. Their sense of law and order, their sense of ethic is extremely similar to ours, and therefore assimilation into our culture, while remaining separate, has never been an issue.
It is absolutely inarguable that we were born a Christian nation. Others were tolerated if they were peaceful and assimilated into our culture and obeyed our sense of ethics and laws, but to suggest that it was not Christian in every sense, and at every level is to be utterly blind.
The rights of states had to be knocked down in order to institute federally mandated socialism/multiculturalism. You are *for* that?
Have you ever looked at the US Supreme Court building?
Among others, it has a figurine representing, surpise, Muhammad!
Yes, the US was founded as a nation with Religion being separated from the State.
The reasons were many, but one prominent one was that Christianity itself wasn't a single faith- it was/is a collection of various feuding sects, with the feuds often being very violent. The first immigrants to the US fled their homeland on account of these feuds. This is what the Founding Fathers recognised, and realized the utter importance of removing Religion from what constituted the State.