You don’t know what you’re talking about.
USPS Office of Inspector General and Postal Inspectors of the Inspection Service are very much federal agents.
They have federal ID and badges, carry weapons and exercise police powers within their areas of responsibility.
They use the same investigative and interrogation techniques as other cops with the added power of getting people fired as well as prosecuted.
Postal workers dealing with them have to tread carefully and they don’t have a good reputation or record of respecting employee rights.
I know EXACTLY what I’m talking about. I worked for the IRS. They have “Inspectors” just like the Postal Service. They had badges and guns, but not the full LEO respect from the rank and file. They literally were the “Rat Squad”. I’ve know several postal workers and most of them had plenty of stories about abusive managers and the Inspectors that covered for those managers. That these two goons tried to intimidate the whistle-blower shows what cloth they are cut from.