This is only the second Calvin Coolidge biography I have read, but it was far more insightful. It concentrates on who Coolidge was as a human being rather than on his political career. In popular history, President Coolidge's personality during his presidency (1923-28) was dour and of few words; politically, he was unusually detached, passive and even disinterested in everything going on in the country and the world.
Author Robert Gilbert's thesis is an explanation for that. Calvin Jr., the younger of he president's two sons, died in 1924 after getting a blister, during a tennis match, that became infected. (This was the pre-antibiotics era.) The president and first lady were distraught, of course; but based on Calvin Sr.'s subsequent behavior, Gilbert believes the former never recovered from Calvin Jr.'s death; and specifically, that he was disabled by major depression (due to unresolved grief) for the rest of his presidency and beyond. This ruined his presidency and made him decline to run for reelection.
Besides the behavior he became most famous for--sleeping most of the time, which is a symptom of depression--and general passivity, the book states that he started displaying strange and unpleasant behaviors with everyone--Mrs. (Grace) Coolidge, his surviving son (John), his Secret Service men, the entire White House staff, etc. His physicians believed he was having (or approaching) a mental breakdown, and didn't understand that it was a crippling episode of depression.
I'd like to own this book, but it's hard to find (probably due only to limited printing) and expensive. (I got it on interlibrary loan.)