Rough Terry stop explained.
police will try and finesse "Terry v. Ohio". If they see a handgun in plain view, it meets Terry's first prong (sort of) that there's a "reasonable articulable belief that you're presently armed and dangerous." It's that last word that trips them up: just because someone is armed at a traffic stop does not, without other facts, make someone dangerous.
The second prong of Terry tends to be a problem for LE as well. They have to have a "reasonable articulable belief that criminal activity is afoot". A traffic stop, generally, does not give rise to anything meeting the second prong. However, the traffic violations that ooze into criminal offenses, lime DUI and reckless driving, can meet the second prong test.
Like I said the JSO tried to turn a traffic stop into a fishing/Terry stop and failed