[Joseph Loconte is a senior fellow at Pepperdine University's School of Public Policy, where he writes widely about the role of religion in promoting democracy, human rights, and social justice. He is the editor of "The End of Illusions: Religious Leaders Confront Hitler's Gathering Storm."]

The American presidency has been described as the most powerful political office in the world. Perhaps in no other Western democracy does the position of president occupy the singularly important role that it does in the United States. The head of the Executive Branch of government, defender of the Constitution, Commander in Chief of the Armed Forces—the American president assumes all of these roles and more. He serves as the living symbol of the nation’s democratic values. Though easily overlooked, some of America’s most beloved presidents have been men of deep religious conviction. They have shaped not only the national character, but also America’s image and influence before a watching world...