After Abraham Lincoln's assassination in 1865, William H. Herndon began work on a brief, "subjective" biography of his former law partner, but his research turned up such unexpected and often startling information that it became a lifelong obsession. The biography finally published in 1889, Herndon's Lincoln, was a collaboration with Jesse W. Weik in which Herndon provided the materials and Weik did almost all the writing. For this reason, and because...