The best security would begin with what you suggest, but I would go much further. While it limits the number of venues for the event, the results will be much better for both the speakers and the audiences.
Start with underground or elevated parking adjacent to the venue, which allows for screening of vehicles, vehicle security when parked, and secondary screening from the parking area into the building.
The auditorium should be “three segments back” from entrances, say a lobby, a secondary room, and then the auditorium. This provides protection from both vehicular attack and noise.
Last, but not least, having a couple snipers on nearby rooftops is always good. They, and a few people with walkie-talkies to act as “pickets” to spot large mobs approaching, and you should be good to go.
like it. Send it on to your congress critter, a repub hopefully.
At the very least, these meetings should be for constituents only (might not help senators, but would help reps.) Photo ID required at the door to prove the person lives in the district.