[A]ll history is a witness of the truth of the principle that good morals are essential to the faithful and upright discharge of public functions. The moral character of a man is an entire and indivisible thing—it cannot be pure in one part and defiled in another. A man may indeed be addicted, for a time, to one vice and not to another; but it is a solemn truth that any considerable breach in the moral sense facilitates the admission of every species of vice. The love of virtue first yields to the strongest temptation; but when the rampart [resistance] is broken down, it is rendered more accessible to every successive assailant… Corruption of morals is rapid enough in any country without a bounty [an encouragement] from government. And… the Chief Magistrate of the United States [the President] should be the last man to accelerate its progress.
Noah Webster, essay on this topic (why a high level of morality was necessary in the Presidency) written in 1801, as referenced in Original Intent: The Courts, The Constitution, and Religion, by David W. Barton, Wallbuilder Press, 1996