Nice short book of 102 pages by F Lauriston Bullard, copyright 1915.
Focuses on the years after Willie died, and the close relationship between Tad and his father, and how important they were to each other in supplying emotional support to each other. A touching tribute to them both. I thought it was a good read. Available on line at
https://archive.org/details/tadhisfather00bulla
The real reason I purchased and read the book is the following interesting article about the author from the Journal of the Abraham Lincoln Association.
http://quod.lib.umich.edu/j/jala/2629860...on+bullard
After reading that, I wanted to own a book he had written. I was able to find a copy in good condition for only $2.