The teachings of the Bible are so interwoven and entwined with our whole civic and social life, that it would be literally – I do not mean figuratively, I mean literally – impossible for us to figure to ourselves what that life would be if these teachings were removed. We would lose almost all the standards by which we now judge both public and private morals; all the standards toward which we, with more or less resolution, strive to raise ourselves.
– Theodore Roosevelt (1858-1919), 26th president of the United States
Source: U-Turn: Restoring America to the Strength of its Roots by David Barton and George Barna, Frontline, 2014, page 103.
For an extensive list of quotes like this from American leaders, see Historic Quotes About the Bible.