The books: Ulysses S. Grant by Josiah Bunting III and Ulysses S. Grant: The Unlikely Hero by Michael Korda.
The warning signals:
Michael Korda is not concerned with writing a revisionist history ... Korda evaluates Grant's presidency as a failure. He cites the historian Allan Nevins' notion that Grant considered "the presidency as a reward, not a responsibility."
Although Bunting is attempting to write a revisionist history of Grant's presidency ... Bunting's book will not cause scholars to change their evaluation of Grant as one of the worst presidents in U.S. history.
It's a commentary on the state of Civil War studies that biographers still rely on Nevins' polemical, six-decades-old work for insights about Grant. Sad also, that a revision falls flat because the writer chooses merely to issue pronoucements on historical issues instead of working through the contrary evidence. That was Nevins' way too and the point of revision is to be a better historian than Nevins, Catton, Sears, or McPherson by respecting all underlying material and allowing it to shape your opinions.
Jean Smith is among the Grant revisionists, rehabilitating his contributions to Reconstruction; he follows the crowd on matters of Grant's permissiveness, however. (Korda is Smith's editor at Simon and Schuster, by the way.)
On the corruption side, there does not seem to be an effective voice striking down the more extravagant nonsense or aggressively defending Grant's management of his Cabinet. Or do I need to broaden my reading?
Meanwhile, assumptions about the corruption of the Grant administration have so permeated the general culture as to supply a motif for comic operas.