I just added Zero Fail: The Rise and Fall of the Secret Service by Washington Post writer Carol Leonnig to the Recommended Reading List.
In it, the always understated Leonnig explores the Secret Service concentrating on the period of the JFK to the Trump administrations. It will go down as the seminal book on the agency. Typical of big business and government agencies it has a lot of problems. It is under resourced along with a lot of “old boy” and CYA culture issues typical of many police organizations.