It is not illegal to record a public employee in a public place. The government does not operate in secret.
“...congressional staffer in his office...” Would someone’s private office qualify as as a public place?...even in Maryland?....Would you know the relevant MD law on this? Thanks.
I'm in a one party consent state. Consequently at work I've become used to people trying to quietly record or sticking their phone in my face to record me trying to get a reaction when they can't get their way because we've chosen to follow the law and/or policy. I don't have time for their games and don't play with them.