Andrew Ferguson toured America to see how we commemorate Honest Abe. He reports on his travels in Land of Lincoln.

You write that Lincoln is a mirror of the culture wars. How so?

Americans' changing understanding of ourselves is reflected in our changing understandings of Lincoln. The most obvious example is C.A. Tripp's trying to prove Lincoln was homosexual [in The Intimate World of Abraham Lincoln]. Another recent book argues that Lincoln's greatness resided in his depressive temperament. We're now obsessed with sex, so we come out with something on Lincoln's sex life. We're obsessed with people's interior psychology, so we argue that Lincoln was manic-depressive. What I try to show in the book is that there's a kind of Lincoln that survives all our parochial interpretations of him.

How is Lincoln remembered in African-American communities—as the Great Emancipator or as a conservative Whig who was openly racist?

The majority view now is that he was largely irrelevant, that in fact the slaves freed themselves. He was not a racial liberal in the 20th-century sense. On the other hand, it's not by accident that Barack Obama chose to announce his presidential candidacy at the Old State Capitol in Springfield [Ill.], where Lincoln delivered one of his greatest speeches. It suggests that Lincoln still has something to say about our contemporary racial situation.

How is Lincoln remembered by the Republican Party of today?

Lincoln remains a powerful figure, as one of the last few remaining popular Republicans. It's also true that a lot of the Bush people, by calling themselves big-government conservatives, think they are invoking a tradition Lincoln founded of governmental activism, of an executive who intervenes to the advantage of one party or the other. I think that's a total misunderstanding of Lincoln's conception of government, but it's a useful rhetorical trick for Bush Republicans to use.

After all your travels through "Abe's America," what do you conclude is the essence of Lincoln's greatness?

Lincoln's greatness lies in the particular kind of union that he preserved. He rededicated this United States to its founding principle that all human beings are created equal. If he hadn't succeeded in what he tried to do, that fundamental principle would have slipped away. The fact that he didn't fail means the principle survived. What greater contribution is there? I wrote the book in part because I want us not to forget Lincoln. He was the best of us in the deepest way.