From The Washington Post:
President Buchanan is reported to have said to President-elect Lincoln as they rode down Pennsylvania Avenue on the latter’s Inauguration Day: “My dear sir, if you are as happy on entering the White House as I shall feel on returning to Wheatland [Buchanan’s Pennsylvania home], you are a happy man indeed.” But Abraham Lincoln did not expect to attain “happiness” in the White House or, as this intellectually energetic book shows, anywhere else. Lincoln’s Melancholy sounds again the half-forgotten, minor-key background music of his life. Joshua Wolf Shenk rejects the notion that Lincoln got over his melancholy under the demands of the presidency; his Lincoln is never too busy to be gloomy. And, drawing on modern studies of depression, Shenk even has a reference — humorous, I think — to “happiness” as a mental disorder.
More here.