Decades ago, the distinguished Lincoln biographer David Herbert Donald coined the phrase “getting right with Lincoln” to describe the impulse people feel to appropriate Lincoln for their own political agendas. Anyone who has watched Barack Obama, who as a senator wrote an essay for Time magazine entitled “What I See in Lincoln’s Eyes” and swore the oath of office as president on Lincoln’s Bible, will be familiar with the phenomenon. Democrats like to claim Lincoln as, in effect, the first Big Government liberal, while Republicans tout him as the founder of their party. But the reflex identified by Donald isn’t...