When a president takes the oath of office, he swears to "preserve, protect and defend the Constitution." Based on that duty, Abraham Lincoln exerted more power than any previous president. He made full use of the broad Constitutional authority given to the president in case of a national uprising. He helped preserve the United States and brought about the abolition (end) of slavery.

As a self-made man leading a self-governing nation, Lincoln became a folk hero. Tales continue to be told, from stories of his humble, backwoods upbringing to examples of his leadership during the Civil War (1861-65), the nation's greatest crisis. He is the president most often written about and studied.

Ambitious and willful, Lincoln was a skilled speaker and a clever politician. He always seemed to know exactly when to be most forceful and when to wait for a better opportunity. For example, he...