On July 4, 1864, four days after President Abraham Lincoln had surprised him by accepting his resignation, Treasury secretary Salmon P. Chase confided to his diary, “I am too earnest, too antislavery … [and] too radical.” Chase surely possessed each of these attributes – in excess – but they had little to do with his unexpected exit from Lincoln’s “team of rivals.” Rather, it was much more personal. Chase’s oft-repeated threat to quit had tested the forbearance of a beleaguered president once too often. Out of patience, Lincoln ended his tenure with the observation that “you and I have reached...