The people who founded this nation had no conception of what "white" or "Christian" meant in the context in which those words are used in America today. They would have thought of themselves (perhaps) as puritans, protestants, or whatever, and if they had a thought of race it would be "English" rather than "white."

Whiteness is a construct of the 20th century, particularly 20th century America. 100 years ago the elites of American society wouldn't have thought of themselves as "white" but rather "Anglo Saxon protestant" to distinguish themselves from the Catholic "other."

It's absurd to use a 20th century concept to categorize people 200 years ago who would have had no meaningful self-identification as such.