While sound would be nice, after watching it a few times the body language of the idiot was all I needed to see to not be surprised the Guard is being charged with a crime. The LEO is trying to leave, Barney has his gun out and is then trying to stop the LEO with gun in hand. This is a great way to have a disastrous accidental discharge. If the building was being guarded by Federal Cops I would hope you would not see this kind of show. If Barney told the LEO he could not carry and LEO told him to F off even, then call 911 and tell them some guy dressed as a Cop, is refusing to follow my authority. When guy dressed as a Cop is leaving? Let him go. It is amazing he did not touch off a round. It is also amazing to me that some want to defend Barney. The IRS needs to budget enough money to have off duty LEO's as guards there, or it they really insist on armed guards pay enough to have pro's. There are a LOT of places that hire LEO's who are retried or on days off for this who would not have done this.
Do we know what this guard's training and the IRS/FPS policies are? Perhaps his instructions were to detain someone who brings a weapon into the building. He might have been told to use the gun he was given if needed.
When the deputy simple ignored him and walked away he was probably confused- I would bet he wasn't told how to handle someone in a uniform saying "I'm a cop, you can't make me." Looks to me in that video like he is someone struggling to do his job and follow instructions but not clear on how far he can escalate if the offender refuses to comply.
Again, the deputy was on federal property violating federal law. Maybe it was an honest mistake but, as someone who deals with the law daily, he should know better than to think he can just leave without repercussions.