This whole thing sounds way out of porportion.
So the cop is assigned to the airport. Mon-Fri he walks around armed. Sunday he (as cops are supposed to be) is armed when off duty and is now a threat to aviation security? Pathetic. At least they didn't dump the terminal.
The only issue I see that could be a problem is the cop -- unticketed -- was allowed to escort family members to the gate. As a normal Joe Citizen, I have to kiss them good bye at the security checkpoint. I see that all the time at DCA too; well-dressed Feds meeting family members at the gate when normal people have to wait for them after the leave the security area.