Few expected politician Abraham Lincoln and Congregational minister Owen Lovejoy to be friends when they met in 1854. One was a cautious lawyer who deplored abolitionists' flouting of the law, the other an outspoken antislavery activist who captained a stop on the Underground Railroad. Yet the two built a relationship that, in Lincoln's words, was one of increasing respect and esteem. In Collaborators for Emancipation: Abraham Lincoln and...