If this keeps happening, maybe the NRA should consider offering firearms storage lockers for these meetings. In PA, courthouses are required to provide firearms storage if you need it when entering. These could be very much like many police stations have for officers entering an area where prisoners maybe kept.
I think the NRA could even get it sponsored so it would not cost them anything.
Anyplace I am expected to sacrifice my personal liberties is a place I won’t frequent. I’ll make an exception for when I am taken by ambulance to a hospital, but otherwise, POTUS or not, tough.