The trouble with this guy was that his paperwork wasn't right and then he became pushy and demanding, fitting the profile of someone who was trying to bully an aircrew in letting him on the aircraft. You would think a Secret Service agent would have the smarts to not give the captain a reason to question his authenticity. Quite simply, this guy's paperwork was not exactly right AND his attitude and demenor did not match that of the professional he was purporting to be.
Now, if the incompetent leadership in the FAA and government would do what ALPA has been asking for since 1989 - that is, issuing ELECTRONICALLY verifiable, POSITIVE identification, a lot of these problems would simply GO AWAY. But, that would take foresight, initiative, and leadership . . . none of which are qualities possessed by the administrator of the FAA.