New York Times best-selling author Stephen Mansfield's latest book is "Lincoln's Battle With God." A former pastor and radio show host, he's written biographies on Winston Churchill, George Whitefield, President Obama, President George W. Bush and Booker T. Washington. Mansfield describes himself as a Christian and lives in both Nashville, Tenn., and Alexandria.

Your book describes Abraham Lincoln as a young atheist who eventually becomes a believer in God and an author of some of the most poetic theological statements we have in American political speeches. What were the key turning points in that transformation?

He was raised by parents who were very much caught up in the revivals of the Second Great Awakening, and he was kind of turned off by what we wouldn't even call Pentecostal -- it was more extreme than that. And he had a terrible relationship with his father. He started that process of self-education, and he began to devour books; some of what he devoured was religious skepticism. Authors like Edward Gibbon, Thomas Paine -- he really drank it in. He spent about a decade as the village atheist, writing tracts and pamphlets.

What really turned him back on the pursuit of God was years later, in 1850, his child Tad died. Lincoln had always suffered from depression -- he had tried to commit suicide a couple times -- and he really needed some help. So he reached out to a Presbyterian pastor in town, and this guy did two things: He comforted him in his grief, and he answered all of his intellectual questions. That's what turned him on to the journey of faith he was on the rest of his life. We know one of the last things he ever said was that he wanted to walk in the Holy Land "in the footsteps of the Savior." I don't paint him as an evangelical Christian, but he was a believer in God, and thought of the Civil War as judgment of the nation, and things like that.

You've written several books on the faith of leaders -- Winston Churchill, Barack Obama, George W. Bush. What have you found in the lives of these men to inspire your own?

All of them had seasons of really seeking God or trying to find out if there was a God or spiritually pursuing that were very moving. None of them came to faith easily, not Bush, not Obama, not Lincoln. They all had good questions and good intellects and were taught by somebody at some point to doubt religion, and they all had to dig their way back. I think what's most inspiring to me is they didn't put up with easy answers. And the other thing is that their faith shaped their policies. Even though they were different men with different theologies, each of them was doing things dictated by his faith. Lincoln certainly did. Even the Emancipation Proclamation was based on a covenant he made with God -- he told his Cabinet that.

At your core, what is one of your defining beliefs?

All men and women of every color and nationality and type are made in the image of God, and they have "eternity in their hearts." That's a quote from Ecclesiastes. In other words, they have a dynamo in their hearts that's drawing them to faith and God.