Ever heard of checking an officials ID with his picture on it or do you have them in your state? Besides, before Trump comes to town the SS has confided and communicated with local law enforcement officials rather extensively.
Ever hear of assassins using uniforms and fake IDS before? The cop was not barred, his having a gun without being cleared to be within shooting distance of Trump was the issue. Not his uniform. A good cop without an anti-Trump Agenda knows the actions of the SS were justified and SOP. So his refusing to check his weapon and make a pubic issue over it is telling about this cop and his agenda. Good call by the SS.