RAY SUAREZ: Who was Abraham Lincoln, the public and the private man? Just what is it about this former president that makes him such a compelling and intriguing figure to so many, even today?
With us to shed some light on Lincoln is David Herbert Donald, a Pulitzer Prize-winning historian and Lincoln biographer. He's a professor emeritus of American History at Harvard University.
Professor Donald, so much American History has happened since that day in Ford's Theater. The country became a globe-straddling world power, two world wars, a Depression. Why is it essential to understand Abraham Lincoln today?
DAVID HERBERT DONALD: I think it is because Lincoln set the tone that America has followed and should follow ever since. That is the dedication to republican principles, the dedication to equality, the dedication to upholding the Declaration of Independence. These are the things he stood for, and as long as we remember them, we are still on the right track.
RAY SUAREZ: When you look at the dozens of men who've held the office, why is it that Lincoln after all this time is still so present in pop culture, in political cartooning, in commercial products, in jokes that people tell even?
DAVID HERBERT DONALD: Well, let's think of the other possibilities. Could you think of making sort of a big museum about Millard Fillmore, for example, or James A. Garfield? Lincoln occupies such a strategic place in American history. Washington got the country off to a start, but it was Lincoln who saved the union, and that saving of the union coupled with the emancipation of the slaves meant that his name was going to last forever.
And when you add to that that he was able to express his views in language that no other American president -- indeed hardly anyone else ever-- was able to equal. There's no other president who is so quotable, whose words resonate down until today. This is something you cannot say of other American presidents, and this is why he lives on...