Wrong, it’s not Protestant Christians who are responsible for the fall of America; it’s the secular left, numbscull. If you want to get technical about it, American Catholics (per survey results) are more liberal than American Protestants.
The point of the story is protestants got their beliefs on morality from the Catholic Church, then because there is so many different denominations in protestantism, having wildly different views, with no doctrine whatsoever to tell them what’s right and wrong, Christianity has went to hell in a hand basket in this country.
And it is the rejection of the most fundamental distinctive of the Reformation, that of Scripture as supreme as the wholly inspired and accurate word of God, that is a fundamental aspect of secularism.