I'm amazed how many people think "separation of church and state" is in the US Constitution, or that it was the theory behind the 1st Amendment, or that it was America's founding "purpose," or that the founders generally believed in it.

None of this is true.

If any of you are interested in learning the actual history of the theory of "separation of church and state" in America, Philip Hamburger of Columbia Law School wrote the best book on the subject: https://www.amazon.com/Separation-Church-State-Philip-Hamburger/dp/0674013743

The bottom line is that "separation of church and state" didn't become the law of the land in the United States until the Supreme Court's decision in Everson v. Board of Education applied the 1st amendment to the states. That was in 1947.

https://en.wikipedia.org/wiki/Everson_v._Board_of_Education

Everson was part of a larger move to impose Enlightenment liberalism as the de facto national philosophy or religion after World War II.

"Separation of church and state" was a fundamental tenet of post-WWII liberalism, not of America.

During WWII, Roosevelt still thought that America was fighting for Christianity and democracy.

For more on the rise of Enlightenment liberalism in America after Roosevelt, take a look here: https://americanmind.org/essays/conservative-rationalism-has-failed/