The President's Henchman is the first in the Jim McGill series by Joseph Flynn. The first few titles in this series were conventionally published before Flynn created his own Stray Dog Press, about which you can make your own decision as to whether it is self-pub or not. I have however, read and enjoyed almost all of the books in this series as well as some books in a spin-off series.
Henchman is free right now as the BN Readouts free weekend reading, and is also free at Kindle and Kobo US.
Kindle US:
https://www.amazon.com/Presidents-He...dp/B00DPYK8KK/
Kobo US:
https://www.kobo.com/us/en/ebook/the...t-s-henchman-2
BN US:
https://www.barnesandnoble.com/w/pre...=2940158986178