I’m only up to the year 1895 in listening to John Taliaferro’s All the Great Prizes: The Life of John Hay, but it’s clear that what others are seeing as a bug in the biography is something I’d call a feature: its focus on the literary rather than the political side of Hay’s life.  Historians like Louis L. Gould in the Wall Street Journal and Heather Cox Richardson in the Washington Post have faulted Taliaferro’s lack of emphasis on politics, but for the literary historian, it offers a passing parade of nineteenth-century characters:

• The Five of Hearts, including Henry Adams, the tragic Clover Adams, subject of a fine recent biography by Natalie Dykstra; and the mercurial Clarence King, whose amazing double life is told in Martha Sandweiss’s fascinating social history and biography of King, Passing Strange. 
• The usual suspects: Lincoln, for whom (as anyone knows after seeing Lincoln), Hay served as a private secretary with John Nicolay; Garfield, Grant, James G. Blaine, McKinley, Mark Hanna.
• Our old friend W. D. Howells, with whom Hay shared a lively correspondence as both men seem to have done with everyone else in the nineteenth century.
• The beautiful and elusive Lizzie Cameron, for whom Hay, Adams, and a good portion of nineteenth-century masculine Washington seem to have carried a considerable torch (was she the “It Girl” of the Gilded Age?). She deserves a biography of her own.
• Directly or indirectly: Mark Twain,  Henry James, and Bret Harte.  The latter’s success inspired Hay to write two popular dialect poems, “Little Breeches” and “Jim Bludso of the Prairie Belle.” 
• And Constance Fenimore Woolson, the subject of Anne Boyd Rioux’s new biography project.  Hay was related to Woolson through Samuel Mather, and it was Hay who helped arrange and pay for her burial in Rome’s Protestant Cemetery. To Henry Adams, he wrote (I’m paraphrasing): “We buried poor Constance Woolson today. She did much good in her life, and no harm, and she had no more happiness than a convict.”

Hay’s The Breadwinners, which I read many years ago, is discussed at some length, as is the LIncoln biography and Hay’s poetry.