A president who governed a divided country has much to teach us in a twenty-first-century moment of polarization and political crisis. Abraham Lincoln was president when implacable secessionists gave no quarter in a clash of visions inextricably bound upwith money, power, race, identity, and faith. He was hated and hailed, excoriated and revered. In Lincoln we can see the possibilities of the presidency as well as its limitations. At once familiar...