Jimmy Carter, probably. It’s impossible to know the contents of a man’s heart, but historians who study the religious lives of the presidents point again and again to the words and deeds of James Earl Carter Jr. The Georgia Baptist set a new standard during his 1976 presidential campaign when he described himself as “born again,” and he was frank about his religious beliefs throughout his presidency. While in office, Carter attended church wherever he went, even while on the road, and continued to teach Sunday school when at home. He prayed daily and read the Bible, and when he wasn’t reading the Bible he read theologians like Reinhold Niebuhr. Like Romney, he also knocked on doors as a missionary, addressing potential converts by saying, “I’m Jimmy Carter, a peanut farmer. Do you accept Jesus Christ as your personal savior?” Since his presidency he has continued his Christian mission on annual trips for Habitat for Humanity, and when he accepted the 2002 Nobel Peace Prize, he spoke of Jesus Christ as “the Prince of Peace.” His Secret Service codename was “The Deacon.” …

Prior to Jimmy Carter, the most God-fearing U.S. president may have been James Garfield. Garfield is the only president who was actually a clergyman. At a young age Garfield became a minister for the Disciples of Christ, where he was lauded for his skill as a preacher, and he learned Greek—the original language of the New Testament. Though it was not his full-time job, he continued to preach and minister for years until his presidency. When he left his position to become president, he said, “I resign the highest office in the land to become President of the United States.” However, as Garfield only got to be president for six months before his death (he was assassinated by a religious zealot), there wasn’t much time for him to demonstrate divine pursuits while in office.