Abraham Lincoln was apparently one of those men who regarded "connubial bliss" as an untenable fantasy. During the Civil War, he pardoned a Union soldier who had deserted the army to return home to wed his sweetheart. As the president signed a document sparing the soldier's life, Lincoln said: "I want to punish the young man-probably in less than a year he will wish I had withheld the pardon." Based on thirty years of research, An American...